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PubMed2006

AMIGOS: a method for the inspection of genomic organisation or structure and its application to characterise conserved gene arrangements.

In order to identify and to characterise gene clusters conserved in microbial genomes, the algorithm AMIGOS was developed. It is based on a categorisation of genes using a predefined set of gene functions (GFs). After the categorisation of all genes of a genome and based on their location on a replicon, distances between GFs were determined and stored in genome-specific matrices. These matrices were used to identify GF clusters like those strictly conserved in 13 archaeal, in 47 bacterial genomes and in the combination of the sets. Within the combined set of these 60 microbial genomes, there exist only two strictly conserved clusters harbouring two ribosomal genes each, namely those for L4, L23 and L22, L29. In order to characterise less strictly conserved GF clusters, content of genomes i.e. matrices were analysed pairwise. Resulting clusters were merged to (meta-) clusters if their content overlapped. A scoring system named cons(CL) was developed. It quantifies conservedness of cluster membership for individual GFs. For the genome of Escherichia coli it was shown that a grouping of cluster elements on cons(CL) values dissected the clusters into smaller sets. These sets were frequently overlapped by known transcriptional units (TUs). This finding justifies the usage of cons(CL) scores to predict TU membership of genes. In addition, cons(CL) values provide a sound basis for non-homologous gene annotation. Based on cons(CL) values, examples of conserved clusters containing annotated genes and single ones with unknown function are given.

Algorithms↗

PubMed1995

Induction of a primary human cytotoxic T-lymphocyte response against a novel conserved epitope in a functional sequence of HIV-1 reverse transcriptase.

OBJECTIVE: To identify novel major histocompatibility complex (MHC) class I-restricted cytotoxic T-lymphocyte (CTL) epitopes conserved in HIV-1. METHODS: Potential conserved CTL epitopes were selected using a predictive computer algorithm based on a human leukocyte antigen (HLA)-A*0201 peptide-binding motif and tested for actual binding to the human processing defective cell line 174.CEM T2 (T2). Hence, the amino-acid sequences of 14 full-length sequenced HIV-1 strains were analysed. An in vitro primary peptide-specific human CTL response was induced with responding lymphocytes of an HIV-1-seronegative donor. Responding T cells were cloned by limiting dilution and tested for their ability to recognize naturally processed antigen in a 51Cr-release assay using recombinant vaccinia-HIV protein-infected B-lymphoblastoid cells (B-LCL) as target cells. RESULTS: The analysis of peptides bearing the HLA-A*0201 motif for conservation resulted in one peptide of Env, three of Gag and 12 of Pol. Only Gag340-348, Pol83-92, Pol267-277 and Pol960-968 showed binding properties to T2 comparable with those of known CTL epitopes Gag76-84 SLYNTVATL and Pol468-476 ILKEPVHGV. A successful primary MHC class I-restricted CTL response was induced against Pol468-476 and Pol267-277 VLDVGDAYFSV, a peptide in a functional sequence of reverse transcriptase (RT). The resulting CD8+ CTL clones were peptide-specific and able to specifically lyse recombinant vaccinia-HIV-1 RT-infected HLA-A*0201-matched B-LCL. CONCLUSION: The method used to screen proteins sequences for potential CTL epitopes, test selected peptides for binding to MHC class I and induction of an in vitro primary response against optimal binding peptides resulted in the identification of at least one novel conserved CTL epitope. The novel epitope is located in an area crucial for RT activity. This study demonstrates the feasibility of identifying highly conserved HIV-1-derived peptides capable of eliciting novel anti-HIV-1 CTL responses.

Amino Acid Sequence↗

PubMed1994

A class act: conservation of homeodomain protein functions.

Dramatic successes in identifying vertebrate homeobox genes closely related to their insect relatives have led to the recognition of classes within the homeodomain superfamily. To what extent are the homeodomain protein classes dedicated to specific functions during development? Although information on vertebrate gene functions is limited, existing evidence from mice and nematodes clearly supports conservation of function for the Hox genes. Less compelling, but still remarkable, is the conservation of other homeobox gene classes and of regulators of homeotic gene expression and function. It is too soon to say whether the cases of conservation are unique and exceptional, or the beginning of a profoundly unified view of gene regulation in animal development. In any case, new questions are raised by the data: how can the differences between mammals and insects be compatible with conservation of homeobox gene function? Did the evolution of animal form involve a proliferation of new homeodomain proteins, new modes of regulation of existing gene types, or new relationships with target genes, or is evolutionary change largely the province of other classes of genes? In this review, we summarize what is known about conservation of homeobox gene function.

Animals↗

PubMed1994

Identification of conserved amino acid residues in the beta subunit of human choriogonadotropin important in holoprotein formation.

The beta subunits of mammalian glycoprotein hormones contain 20 invariant amino acid residues, including 12 Cys residues that form six disulfide bonds, as well as other highly conserved residues. Such stringent conservation suggests an important role for those residues in chain folding, holoprotein formation, or receptor binding/activation, but not receptor specificity. Using site-directed mutagenesis, we have prepared and characterized replacements of 14 conserved non-Cys residues in human choriogonadotropin beta for which there is little, if any, information available: Pro7, Thr32, Tyr37, Thr40, Val56, Tyr59, Phe64, Pro70, Gly71, Ser81, Tyr82, Val84, Ala85, and Ser87. The cDNAs were subcloned into a pRSV mammalian expression vector and transiently transfected into Chinese hamster ovary cells containing a stably integrated gene for bovine alpha. Holoprotein formation was assessed by radioimmunoassays, and in vitro competitive binding and steroidogenic assays were used to determine potencies. Our results demonstrated that Tyr37, Thr40, Tyr59, and Ala85 participate directly or indirectly in holoprotein formation, as may Ser81. Replacements of the other conserved amino acid residues resulted in no significant change in subunit assembly or receptor binding/activation as measured, although an Arg at position 81 or 82 reduced secretion. This study has identified several amino acid residues of the beta subunit that are important in alpha binding and has raised interesting questions on the constraints that maintain conservation of amino acid residues during evolution.

Amino Acid Sequence↗

PubMed1993

Functional analysis of conserved residues in the active site of insulin-degrading enzyme.

Insulin-degrading enzyme (IDE), a nonlysosomal metalloprotease involved in metabolizing internalized insulin, has catalytic properties that have been strongly conserved through evolution. Two major properties distinguish IDE from the prototypic metalloprotease thermolysin. 1) It is inhibited by cysteine protease inhibitors as well as metalloprotease inhibitors; 2) it contains an inversion of the HEXXH active site motif of thermolysin, where the histidines coordinate zinc and the glutamate participates in catalysis. Furthermore, cysteine is adjacent to the glutamate residue (HXCEH) in human, rat, and Drosophila IDE, although it is not conserved in their close homologue, Escherichia coli protease III. This cysteine has been postulated to mediate the differential sensitivity of IDE and protease III to cysteine protease inhibitors and chelators. The role of the cysteine in IDE catalysis and inhibitor sensitivity was examined by mutating Cys110 to glycine or serine. To determine whether glutamate in this unusual motif participates in catalysis, we mutated Glu111 to aspartate, valine, or glutamine. Vectors containing wild type or mutant enzymes were transfected into COS cells, and expression was confirmed by Western blotting. Although the glutamate mutants were devoid of insulin degrading activity, the cysteine mutants were indistinguishable from wild type enzyme in both catalytic activity and sensitivity to inhibitors. The loss of activity in the glutamate mutants was not due to gross alterations in tertiary structure, as shown by retention of the ability to bind substrate and by conservative and nonconservative mutation of a neighboring residue with no apparent effect on catalysis. These results demonstrate that the conserved glutamate in the zinc-binding site of human insulin-degrading enzyme is a major catalytic residue, while a conserved cysteine in this region is not essential for catalysis or inhibitor sensitivity.

Amino Acid Sequence↗

PubMed1994

A biological method for examining the effect of codon changes in a conserved region of DNA polymerase.

The vaccinia virus genome encodes a DNA polymerase that is similar to other DNA polymerases. A mutation in the polymerase gene at a site that is adjacent to conserved residues allows viral replication in the presence of aphidicolin. Since wild-type virus is converted to aphidicolin-resistance by site-directed mutagenesis, it was feasible that active virus with substituted conserved residues could be detected by linking alterations to the aphidicolin-resistance mutation. Altered DNA, from a PCR, was introduced into virus by a marker transfer procedure. DNA from plaques of drug-resistant virus was amplified, and the product was sequenced to check for the conserved residue alteration. An alteration that introduced a Bg1I site was designed to facilitate the selection of drug-resistant virus containing substituted residues. One positive result was the replacement of two amino acids, tyrosine and alanine, by tryptophan and threonine. The failure to substitute aspartic acid for tyrosine indicates that drastic changes of the conserved sequence are not tolerated. Although the limitations associated with negative results apply, the method provides an in vivo assay for selecting a polymerase with conserved residue changes.

Amino Acid Sequence↗

PubMed1993

Phi 29 DNA polymerase active site. The conserved amino acid motif "Kx3NSxYG" is involved in template-primer binding and dNTP selection.

phi 29 DNA polymerase shares with other alpha-like DNA polymerases several regions of amino acid similarity. Among them, the conserved region characterized by the amino acid motif "Kx3NSxYG" has been proposed to form part of the polymerization active site of alpha-like DNA polymerases. Mutants in phi 29 DNA polymerase residue Tyr390 of this conserved motif had been previously described to be affected in DNA-dependent dNTP binding. In this paper, the functional significance of this conserved motif is further studied by the analysis of mutants in conserved residues Asn387, Ser388, and Gly391. Residue Phe393 of phi 29 DNA polymerase has also been selected as target for site-directed mutagenesis because of its conservation within the group of alpha-like DNA polymerases from genomes that replicate by a protein-priming mechanism. Mutant N387Y was shown to be affected both in initiation and polymerization reactions, showing 3-fold higher Km value for dATP and more than 11-fold lower Vmax value than the wild-type enzyme in the initiation reaction; moreover, it was affected in enzyme-DNA translocation. Mutant S388G retained initiation and polymerization activities; interestingly, this mutation significantly increased the efficiency of dNTP incorporation in non-templated reactions. Mutation Gly391 to Asp abolished template-primer binding as shown by gel retardation assays; this mutant was drastically affected in template-dependent dNTP incorporation both in initiation and polymerization reactions, but the efficiency of the non-templated phi 29 terminal protein-deoxynucleotidylation was higher than with the wild-type protein. Mutation Phe393 to Tyr severely decreased initial binding to template-primer DNA molecules, resulting in a reduced activity in DNA primer-dependent polymerization reactions but not in phi 29 terminal protein-dependent ones.

Amino Acid Sequence↗

PubMed1996

Discovering empirically conserved amino acid substitution groups in databases of protein families.

This paper introduces a method for identifying empirically conserved amino acid substitution groups. In contrast with existing approaches that view amino acid substitution as a pairwise phenomenon, the method presented here identifies conserved groups of amino acids using a data structure called a conditional distribution matrix. The conditional distribution matrix extends the concept of a pairwise substitution matrix by changing the context of substitution from a single amino acid to a group of amino acids. The matrix tabulates information from a database of protein families that contains numerous aligned positions. Each row in the matrix contains the distribution of amino acids in those aligned positions that contain a given conditioning group of amino acids. The method converts a database of protein families into a conditional distribution matrix and then examines each possible substitution group for evidence of conservation. The algorithm is applied to the BLOCKS and HSSP databases. Twenty amino acid substitution groups are found to be conserved empirically in both databases. These groups provide insight into biochemical properties that are conserved in protein evolution.

Algorithms↗

PubMed2006

Pancreatic fistula after distal pancreatectomy: predictive risk factors and value of conservative treatment.

HYPOTHESIS: Predictive factors of pancreatic fistula (PF) and the value of conservative management of PF following distal pancreatectomy (DP) are poorly known. DESIGN: Case series. SETTING: A university hospital referral center. PATIENTS: From 1991 to 2003, 175 patients underwent DP with routine drainage of the pancreatic stump and postoperative repeated measures in drainage fluid. Pancreatic fistula was defined as an amylase level in surgical drainage fluid more than 5-fold the serum level after postoperative day 5, or amylase-rich fluid collection. Computed tomographic scan was only done for suspicion of abdominal collection. Conservative management of PF included percutaneous drainage of abdominal collection and total parenteral nutrition or maintaining oral feeding in some patients with low-volume PF. INTERVENTION: Conservative management of PF after DP. MAIN OUTCOME MEASURES: Incidence of PF according to indication, concomitant splenectomy, additional procedure, texture of parenchyma, location of transection (neck vs body), and technique of stump suture (stapler vs hand sewn), including elective ligation of the main duct, transfusions, and prophylactic use of octreotide. RESULTS: There was no mortality. Forty patients (23%) developed PF, which was symptomatic in 25 patients (63%); computed tomographic scan identified an abdominal collection in 26 (65%). Multivariate analysis identified 2 predictive factors for PF: no elective ligation of the main pancreatic duct (odds ratio, 2.2 [95% confidence interval, 1.0-4.7]) and transection at the body (odds ratio, 2.1 [95% confidence interval, 1.1-5.5]). If none or both predictive factors were present, the observed rate of PF was 16% and 63%, respectively. Pancreatic fistula was managed conservatively in 38 patients (95%), including percutaneous drainage in 16, and by reoperation in 2. CONCLUSIONS: Pancreatic fistula following DP is more frequent in cases of pancreatic division at the body level and no elective ligation of the main duct. Routine drainage of the pancreatic stump does not prevent postoperative abdominal collections. Conservative management of PF is successful in 95% of cases.

Adolescent↗

PubMed1977

Conservative treatment of breast cancer. A trial in progress at the Cancer Institute of Milan.

The report describes a clinical trial on conservative surgery in progress at the National Cancer Institute of Milan, Italy. The randomized clinical trial compares radical mastectomy with a more conservative procedure consisting of mammary resection plus axillary dissection plus radiotherapy. The resection comprises an entire quadrant of the breast together with the overlying skin and the corresponding portion of the fascial sheet of the pectoralis major. The axillary dissection is performed in continuity with the resected breast quadrant except in cases with tumors of lower inner quadrants, who need two separate incisions. After surgery the patients receive 6000 rads to the residual breast tissue over five to six weeks, starting 15 days after operation. The cosmetic results are satisfactory in approximately 70% of cases. The trial is limited to cases with tumors less than 2 cm and no palpable axillary nodes (T1N0M0). Patients with histologically positive lymph nodes (N+) are submitted to adjuvant chemotherapy with CMF for one year. From September 1973, to October 1976, 331 cases entered the trial. One hundred sixty were treated with radical mastectomy and 164 with the conservative procedure. Axillary metastases were found in 23% of the radical and in 29% of the conservative surgery group. Four local-regional recurrences have occurred till now, two in each group. Five cases in the radical mastectomy group and one in the conservative group had distant metastases. The clinical trial will collect some 500 cases by the end of 1977 and significant preliminary results are expected to be available from 1978.

Adult↗

PubMed1985

Role of conserved sequence elements in yeast centromere DNA.

Conserved sequence features in Saccharomyces cerevisiae CEN DNA are confined to a region of approximately 120 bp. The highly conserved 8 bp at the left (PuTCACPuTG) constitute the left boundary of a functional CEN DNA as shown by the analysis of a series of Bal31 deletions. The right boundary of a functional CEN DNA lies within the conserved 25 bp at the right (TGT-T-TG--TTCCGAA-----AAA) or a few base pairs further outside of the 120-bp region. One mutant which just lacks the left conserved DNA element PuTCACPuTG can still assemble into a partially functional mitotic centromere and it assembles into a well functioning meiotic centromere. The sequences between the two conserved terminal DNA elements can be increased in length (+50%) or in GC content (from 6% to 12%) without measurable changes in mitotic and meiotic segregations of plasmids carrying such CEN mutations. The naturally occurring length and GC content of this centromere DNA sequence element is, therefore, not essential for centromere function. We discuss the possibility that it partly acts as a hinge region between two domains. Finally, we tested integrations of CEN DNA into the genome and found a toleration of wild-type CEN6 DNA when present 3' of the LYS2 gene.

Base Sequence↗

PubMed1988

The chicken dystrophin cDNA: striking conservation of the C-terminal coding and 3' untranslated regions between man and chicken.

Dystrophin is a very large muscle protein (approximately 400 kd) the deficiency of which is responsible for Duchenne muscular dystrophy. Its function is unknown at present. In order to know whether different domains of the protein are differentially conserved during evolution, we have cloned and sequenced the chicken dystrophin cDNA. The protein coding sequence has almost the same size as in man. The N-terminal region that resembles the actin binding domain of alpha actinin, as well as the large spectrin like domain show 80% and 75% conservation respectively between chicken and man. In contrast, the C-terminal region shows 95% identity over 627 aa suggesting that it is an important region of interaction with other proteins. Comparison of the amino acid sequence of this C-terminal region to other protein sequences shows only marginally significant similarities. Finally we have found a striking conservation of three segments of the 3' untranslated sequence (85% homology over a total of 920 nt) between chicken and man. These also appear to be conserved in other mammals. This high conservation is not linked to open reading frames.

Amino Acid Sequence↗

PubMed2002

Conservation and variation in enamel protein distribution during vertebrate tooth development.

Vertebrate enamel formation is a unique synthesis of the function of highly specialized enamel proteins and their effect on the growth and organization of apatite crystals. Among tetrapods, the physical structure of enamel is highly conserved, while there is a greater variety of enameloid tooth coverings in fish. In the present study, we postulated that in enamel microstructures of similar organization, the principle components of the enamel protein matrix would have to be highly conserved. In order to identify the enamel proteins that might be most highly conserved and thus potentially most essential to the process of mammalian enamel formation, we used immunoscreening with enamel protein antibodies as a means to assay for degrees of homology to mammalian enamel proteins. Enamel preparations from mouse, gecko, frog, lungfish, and shark were screened with mammalian enamel protein antibodies, including amelogenin, enamelin, tuftelin, MMP20, and EMSP1. Our results demonstrated that amelogenin was the most highly conserved enamel protein associated with the enamel organ, enamelin featured a distinct presence in shark enameloid but was also present in the enamel organ of other species, while the other enamel proteins, tuftelin, MMP20, and EMSP1, were detected in both in the enamel organ and in other tissues of all species investigated. We thus conclude that the investigated enamel proteins, amelogenin, enamelin, tuftelin, MMP20, and EMSP1, were highly conserved in a variety of vertebrate species. We speculate that there might be a unique correlation between amelogenin-rich tetrapod and lungfish enamel with long and parallel crystals and enamelin-rich basal vertebrate enameloid with diverse patterns of crystal organization.

Amelogenin↗

PubMed1986

Sequence conservation and region shuffling in an endoglucanase and an exoglucanase from Cellulomonas fimi.

Cellulomonas fimi produces an endoglucanase and an exoglucanase which bind strongly to cellulose. Each enzyme contains three distinct regions: a short sequence of about 20 amino acids containing only proline and threonine (the Pro-Thr box); an irregular region, rich in hydroxyamino acids, of low charge density, and which is predicted to have little secondary structure; and an ordered region of higher charge density which contains a potential active site, and which is predicted to have secondary structure. The Pro-Thr box is conserved almost perfectly in the two enzymes. The irregular regions are 50% conserved, and the conserved sequences include four Asn-Xaa-Ser/Thr sites. The ordered regions appear not to be conserved, but the potential active sites both have the sequence Glu-Xaa7-Asn-Xaa6-Thr; they occur at widely separated sites in the two regions. The order of the regions is reversed in the two enzymes: irregular-Pro-Thr box-ordered in the endoglucanase; ordered-Pro-Thr box-irregular in the exoglucanase. The genes for the two enzymes appear to have arisen by shuffling of two conserved sequences and either one or two other sequences.

Actinomycetales↗

PubMed1994

Conservative surgical treatment in cervical cancer with 3 to 5 mm stromal invasion in the absence of confluent invasion and lymph-vascular space involvement.

We have previously reported that simple hysterectomy is adequate therapy for microinvasive carcinoma of the cervix with less than 3 mm stromal invasion (Yajima, A., et al, Am. J. Obstet. Gynecol. 135, 685-688, 1979). However, whether it is possible to effectively treat patients with deeper stromal invasion remained in question. A policy for surgical treatment in patients with 3 to 5 mm invasion has not been standardized. Although radical hysterectomy is usually performed, some authors insist that patients with 3 to 5 mm invasion can be safely treated conservatively. Patients treated with conservative surgery should be carefully assessed because cases with confluent invasion or lymph-vascular space invasion have a greater potential for lymph node metastasis and carry a worse prognosis. Conservative treatment in this study was limited to patients with microinvasive carcinoma with 3 to 5 mm invasion, stage IB occult patients (classified by the FIGO 1973 staging system). The patients were preoperatively diagnosed with either carcinoma in situ or microinvasive carcinoma, and treated by conservative surgery (conization, simple hysterectomy, or extended hysterectomy). Twenty-two patients with 3 to 5 mm invasion but without additional risk factors, i.e., confluent invasion or lymph-vascular space involvement, were followed without postoperative radiation therapy. All patients survived except one (who died of an intercurrent disease) and there were no signs of recurrence of serious surgical complications. The present study with stage IB "occ" subjects suggests that conservative therapy rather than radical hysterectomy can be used in a very carefully selected subset of patients, i.e., in cases with 3 to 5 mm microinvasive carcinoma without additional risk factors, such as confluent invasion and lymph-vascular space invasion.

Carcinoma in Situ↗

PubMed1996

Dysgerminoma: the role of conservative surgery.

Twenty-five cases of pure ovarian dysgerminoma treated at UCLA Medical Center between 1958 and 1992 were reviewed retrospectively. Patterns of recurrence and overall survival were analyzed with regard to primary surgery (conservative versus nonconservative), use of adjuvant therapy, and stage of disease. Fourteen patients (56%) underwent conservative surgical therapy defined as preservation of the contralateral ovary, 10 patients (40%) had nonconservative primary surgery, and one patient (4%) had chemotherapy as primary treatment. Three patients (12%) received adjuvant chemotherapy and nine patients (36%) received postoperative radiation therapy. Fifteen patients (60%) had stage I disease, four (16%) stage II, and three each (12%) had stage III and IV disease. Nine patients (36%) experienced recurrence of disease. Seven of these nine patients (78%) had stage I disease and all seven had undergone conservative primary surgery with preservation of the contralateral ovary. Six of the seven had received no adjuvant therapy. Only one of these seven patients experienced recurrence in the preserved ovary. She was found to have a dysgenetic ovary and an XY karyotype. Three patients with recurrent disease had received radiation therapy after primary surgery. Twenty patients (80%) were alive without disease at follow-up, two patients (8%) were alive with disease, and three (12%) had died of disease. There was no statistically significant difference in recurrence rates between those patients treated with conservative surgery and those treated with nonconservative surgery, although the total number of patients with recurrences was greater in the former group. Our data suggest that a conservative surgical approach is the preferred treatment in patients with pure dysgerminoma of the ovary who desire future fertility. Lack of adjuvant chemotherapy or radiation therapy, rather than type of initial surgery, may be associated with a higher risk of recurrence.

Adolescent↗

PubMed1985

Follow-up examinations of conservatively and surgically treated children with hiatus hernia.

Between 1966 and 1976, 65 infants and children were treated because of hiatus hernia. The diagnosis was made radiologically in all cases and in a number of patients endoscopically. 54 patients had a forme mineure (types 1 and 2), and 11 had a forme majeure (types 3 and 4). Of the 20 patients with type 1, 16 (80%) were successfully treated conservatively; two further patients needed a secondary operation. Of 34 children with type 2, 15 (44%) were treated successfully conservatively, and four needed a secondary operation. Of ten patients with type 3, four (40%) were treated primarily conservatively with success. Two children with type 1, 11 with type 2, six with type 3, and one with type 4 had to be operated on primarily because of severe esophagitis at the time of admission. From 14 mon to 10 years after discharge from hospital, follow-up examination of 33 patients showed that one child died from another cause. In 14 of the 21 conservatively treated patients and in 12 of the 18 surgically treated patients (66% in both cases), there were no symptoms or complaints. Eight had subjective complaints, but in only four (10.5%) was there a definite complaint. Three of these four patients had associated diseases (spastic tetraplegia, operated jejunal atresia). In these patients, esophagitis was present on follow-up examination and necessitated further treatment. The treatment of choice for the forme mineure without esophagitis should be conservative, and in most cases this will be sufficient. In only a few of these patients did it become necessary to carry out a secondary fundoplication. Operation is indicated primarily in cases with esophagitis and esophageal stenosis as well as in patients with a forme majeure of the hiatus hernia.

Body Weight↗

PubMed1991

Analysis of conserved domains identifies a unique structural feature of a chloroplast heat shock protein.

A low molecular weight heat shock protein which localizes to chloroplasts has been identified in several plant species. This protein belongs to a eukaryotic superfamily of small HSPs, all of which contain a conserved carboxyl-terminal domain. To investigate further the structure of this HSP, we isolated and sequenced cDNA clones for the chloroplast LMW HSPs from Petunia hybrida and Arabidopsis thaliana. The cloning of chloroplast HSPs from these two species enabled us to compare the amino acid sequences of this protein from plant species (petunia, Arabidopsis, pea, soybean and maize) that represent evolutionarily divergent taxonomic subclasses. Three conserved regions were identified, which are designated as regions I, II and III. Regions I and II are also shared by cytoplasmic LMW HSPs and therefore are likely to have functional roles common to all eukaryotic LMW HSPs. In contrast, consensus region III is not found in other LMW HSPs. Secondary structure analysis predicts that this region forms an amphipathic alpha-helix with high conservation of methionine residues on the hydrophobic face and 100% conservation of residues on the hydrophilic face. This structure is similar to three helices, termed "methionine bristles", which are found in a methionine-rich domain of a 54 kDa protein component of signal recognition particle (SRP54). The conservation of regions I and II among LMW cytoplasmic and chloroplast HSPs suggests that these HSPs perform related functions in different cellular compartments. However, identification of the methionine bristle domain suggests that chloroplast HSPs also have unique functions or substrates within the special environment of the chloroplast or other plastids.

Amino Acid Sequence↗