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PubMed2026

Genomic Insights Into Multidrug-Resistant Foodborne Serratia liquefaciens Strains Carrying mcr-9 and Comparative Genomic Analysis of Novel Biosynthetic Gene Clusters.

Serratia liquefaciens is an opportunistic nosocomial pathogen with a wide range of antibiotic resistance patterns. This study reports the characterization of the first mcr-9-positive S. liquefaciens strains, 35E-19E1 and CST-066, isolated from meat products in Japan. The strains were screened for the presence of β-lactamases, plasmid-mediated mobile colistin resistance (mcr) genes, and carbapenemase-encoding genes using PCR. Antimicrobial susceptibility was tested using the broth microdilution method. The strains exhibited multidrug resistance (MDR) phenotypes to third-generation cephalosporins, cephamycin, fosfomycin, and other clinically important antimicrobials. Genomic DNA sequencing showed that the genome sizes of CST-066 and 35E-19E1 are 5,529,704 and 5,261,506 bps, respectively. mcr-9 was identified on a chromosome within a genetic environment that included the two-component system qseBC, which plays a key role in the signaling network that triggers colistin resistance in Enterobacterales. Downstream genome analysis revealed a 1695-bp eptB-like kdo2-lipid phosphoethanolamine transferase, which is involved in intrinsic polymyxin resistance mechanisms in Serratia spp. The strain 35E-19E1 carries five CRISPR-Cas enzymes that are essential for adaptive immunity in bacteria, allowing defense against invading elements. Functional analysis using subsystem technology revealed that both strains possess subsystem features responsible for invasion and adhesion within the host biomes. Genome mining using antiSMASH and BAGL4 revealed various biosynthetic gene clusters, responsible for secondary metabolite synthesis. Notably, we identified novel gene clusters, mainly nonribosomal peptide synthetases, in both the strains, indicating their potential to produce bioactive compounds. Although the presence of mcr-9 in Serratia may not be of clinical significance because of natural resistance of the strain to polymyxins, we shed light on the genomic characteristics of this MDR pathogen and the potential spread of mcr-9 among other bacterial species. The emergence of mcr-9 in drug-resistant S. liquefaciens provides significant insights, underscoring the need for increased surveillance of this pathogen.

biosynthetic gene cluster↗

PubMed1992

Complexity of FGF receptors: genetic basis for structural diversity and functional specificity.

Since 1989, the receptors for fibroblast growth factors (FGFs) were cloned and characterized as a subgroup of the family of receptor tyrosine kinases. Four FGF receptor genes were identified, all of which encode membrane-bound glycoproteins containing three immunoglobulin (Ig) -like domains at the extracellular region, where only two of these domains are involved in ligand binding. Three unique features characterize the FGF receptors: 1) overlapping recognition and redundant specificity, where one receptor may bind with a similar affinity several of the seven known FGFs and one FGF may bind similarly to several distinct receptors. 2) The binding of FGFs to their receptors is dependent on the interaction of FGF with cell surface heparan sulfate proteoglycans. 3) A multitude of isoforms of cell-bound or secreted receptors are produced by the same gene. The gene structure of these receptors revealed two major mechanisms that are responsible for the formation of the diverse forms: alternative mRNA splicing, resulting in deletions or alternate exons usage, and internal polyadenylation, resulting in truncated products. These are reminiscent of mechanisms that also operate in the immunoglobulin family to generate diversity and to produce either secreted or cell-bound molecules. Tissue-specific alternative splicing in FGF receptors allows for the generation of two distinct receptors from a single gene because alternative exons determine the sequence of the COOH-terminal half of the third Ig-like domain involved in ligand binding. This represents a novel genetic mechanism to generate receptor diversity and specificity and to increase receptor repertoire.

Animals↗

PubMed1987

Structure and expression of pea mitochondrial F1ATPase alpha-subunit gene and its pseudogene involved in homologous recombination.

We have characterized four pea mitochondrial DNA segments carrying the F1ATPase alpha-subunit coding sequences. These four types share a common 1.7-kb repeat sequence flanked by four combinations of two different left- and right-hand sequences. These results suggest that the alpha-subunit genes locate at the homologous recombination sites in the pea mitochondrial genome and that homologous recombination between two of these loci generates the other two types of structures. The uninterrupted alpha-subunit coding sequence of 1,521 bp is present in two of these loci. A rearrangement of 965 bp 3' to the ATG initiation codon generates two copies of pseudogenes where the C-terminal two-thirds of the alpha-subunit coding sequence is replaced with an unidentified coding frame. The other border of sequence divergence is located 733 bp upstream of the ATG initiation codon. Although multiple forms of alpha-subunit gene transcripts are present in mitochondria, the pseudogenes do not seem to express any alpha-subunit-related polypeptide.

Amino Acid Sequence↗

PubMed1990

The Arabidopsis thaliana plasma membrane H(+)-ATPase multigene family. Genomic sequence and expression of a third isoform.

The plasma membrane of higher plants contains a H(+)-ATPase as its major ion pump. This enzyme belongs to the P-type family of cation-translocating enzymes and generates the proton-motive force that drives solute uptake across the plasma membrane. In Arabidopsis thaliana the plasma membrane H(+)-ATPase is encoded by a multigene family (Harper, J. F., Surowy, T. K., and Sussman, M. R. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 1234-1238). The complete genomic sequence of a third Arabidopsis H(+)-ATPase isoform (referred to as AHA2) is presented here, and the predicted protein sequence is compared with previously published AHA1, AHA3, and tobacco Nicotiana plumbaginifolia NP1 isoforms. The AHA2 gene is most similar to AHA1, with predicted proteins containing 95% amino acid identity. The mRNA start site and 5'-untranslated sequence for AHA2 were determined from cDNA amplified by the polymerase chain reaction. The 5' region contains a 23-base pair (bp) polypyrimidine sequence and a short upstream reading frame. In comparison with the 16 introns reported in AHA3, AHA2 is missing one intron in the 5'-untranslated region and a second intron in the C-terminal coding region. An unusually large intron for Arabidopsis (greater than 1000 bp) is present at the beginning of the coding sequence of both AHA2 and AHA3. In the 3'-untranslated sequence of AHA1 and AHA2 but not AHA3, there is a 65-bp region of 85% identity and a second shorter region of 16-bp identity harboring an unusual putative poly(A) addition signal (dTTTGAAGAAACAAGGC). Northern blot analysis indicates that AHA2 mRNA relative to total cellular RNA is expressed at significantly higher levels in root tissue as compared with shoot tissue.

Amino Acid Sequence↗

PubMed1992

Close amino acid sequence relationship between the new plasmid-mediated extended-spectrum beta-lactamase MEN-1 and chromosomally encoded enzymes of Klebsiella oxytoca.

Isolated from an Escherichia coli strain MEN-1 is a plasmid-mediated beta-lactamase that confers resistance to methoxy imino third-generation cephalosporins. The protein purified to homogeneity was digested by trypsin, chymotrypsin and endoproteinase Asp-N. Amino acid sequence determinations of the resulting peptides gave rise to the alignment of the 263 residues of the beta-lactamase. From amino acid sequence comparison MEN-1 was found to share more than 72% identity with the chromosomally mediated beta-lactamases of Klebsiella oxytoca. Therefore, MEN-1 is the first transferable extended-spectrum beta-lactamase which is not directly derived from the widespread TEMs or SHV-1 penicillinases with which it presents less than 39% identity.

Amino Acid Sequence↗

PubMed1991

Mapping using unique sequences.

Theoretical predictions are given for the progress expected, when mapping DNA by identifying clones containing specific unique sequences. Progress is measured in three ways; however, all results depend on (dimensionless counterparts of) the number of clones and the number of unique sequences used. Furthermore, the effects of clone length dispersion are included in the theoretical predictions. Both the clones in the library and the unique sequences are assumed to be generated randomly, with uniform probability of originating at any base in the region to be mapped. The first measure of progress is the expected length fraction of the region to be mapped covered by at least one clone, when clones containing at least one unique sequence are included in the map. The second measure of progress is the expected length fraction of the region to be mapped in "covered intervals", an interval being the region between adjacent unique sequences. Alternative definitions for clones covering an interval are analyzed. The third measure of progress is the expected number of clone islands generated; an island covers successive intervals. Finally, using these measures of progress, we compare the efficiency of this new mapping strategy with conventional clone mapping strategies.

Chromosome Mapping↗

PubMed1986

Mutational analysis of bacteriophage lambda lysis gene S.

A plasmid carrying the bacteriophage lambda lysis genes under lac control was subjected to hydroxylamine mutagenesis, and mutations eliminating the host lethality of the S gene were selected. DNA sequence analysis revealed 48 single-base mutations which resulted in alterations within the coding sequence of the S gene. Thirty-three different missense alleles were generated. Most of the missense changes clustered in the first two-thirds of the molecule from the N terminus. A simple model for the disposition of the S protein within the inner membrane can be derived from inspection of the primary sequence. In the first 60 residues, there are two distinct stretches of predominantly hydrophobic amino acids, each region having a net neutral charge and extending for at least 20 residues. These regions resemble canonical membrane-spanning domains. In the model, the two domains span the bilayer as a pair of net neutral charge helices, and the N-terminal 10 to 12 residues extend into the periplasm. The mutational pattern is largely consistent with the model. Charge changes within the putative imbedded regions render the protein nonfunctional. Loss of glycine residues at crucial reverse-turn domains which would be required to reorient the molecule to reenter the membrane also inactivate the molecule. Finally, a number of neutral and rather subtle mutations such as Ala to Val and Met to Ile are found, mostly within the putative spanning regions. Although no obvious explanation exists for this subtle and heterogeneous class of mutations, it is noted that all of the changes result in a loss of alpha-helical character as predicted by Chou-Fasman theoretical analysis. Alternative explanations for some of these changes are also possible, including a reduction in net translation rate due to substitution of a rare codon for a common one. The model and the pattern of mutations have implications for the probable oligomerization of the S protein at the time of endolysin release at the end of the vegetative growth period.

Alleles↗

PubMed1988

Lessons drawn from observing young peers together.

Based on studies during the past 13 years of what transpires between young peers, lessons are drawn about the nature of human sociability and the development of social skill during the first three years of life. Peer encounters have proven especially helpful for discovering the forms of sociability and social skill the infant is capable of without the aid of a more skillful social partner. From early in infancy, children are quite sociable with peers (age-mates), both in novel play settings and in their own home or customary group care settings, both with an unfamiliar peer and with those quite familiar, both at the start of acquaintanceship with a particular peer and after many encounters with that peer. Their sociability is seen in their attraction to peers, their directing to peers of such distinctively social behaviors as vocalizations, smiles, and gestures, and the predominantly friendly nature of their behavior. Peer encounters in the absence of customary play materials refute claims that attraction to peers is a by-product of interest in toys and the inanimate spectacles peers create through their actions on toys. Distinctions should be drawn between sociability and social skills, especially interactive skills. Interactive skills are systematic ways the young child relates his/her own behavior to the details of a partner's behavior that function to facilitate such valued social outcomes as the generation of a cooperative game or a conversation or the resolution of a dispute. Observations of young peers highlight the distinctive nature of the infant's interactive skills. Social influence between peers is present from 6 months, but rarely takes the form customary for older children. Joining a peer and manipulating the same play material as the peer are rudimentary interactive skills that emerge by 12 months. Interactive skills enabling the generation of extended sequences of social interaction on a common cooperative theme progress rapidly during the third year of life. The distinctive form of the young child's interactive skills produces distinctive patterns of interaction among young peers. Their interactions are managed largely nonverbally well into the third year of life, and extended cooperative interactions most often take the form of games in which one or both children imitate each other's actions. Despite the predominance of imitation, their encounters are also marked by complementary role relationships. The distinctive features of peer encounters prompt speculations about the role peer encounters can play in early development.

Child, Preschool↗

PubMed1992

Cytotoxic T lymphocytes do not appear to select for mutations in an immunodominant epitope of simian immunodeficiency virus gag.

Studies to date assessing HIV escape from CTL in vivo have yielded conflicting results. Previous studies have demonstrated that simian immunodeficiency virus of macaques (SIVmac)-infected rhesus monkeys expressing the MHC class I allele Mamu-A*01 reproducibly develop a gag-specific CTL response limited to a 9-amino acid epitope of the SIVmac gag protein (residues 182-190 within peptide 11C). To determine whether CTL have a role in selecting for AIDS virus mutants, we examined mutations in SIVmac proviral DNA encoding this gag CTL epitope in PBL of infected rhesus monkeys. Three Mamu-A*01+ rhesus monkeys were infected with SIVmac and assessed for gag- and peptide 11C-specific CTL responses. This specific CTL response was maintained in two monkeys, but lost in the third animal 2 yr after infection. The generation of proviral gag mutations was then determined by sequencing 500-bp proviral fragments amplified from fresh PBL obtained from the monkeys more than 2.5 yr after infection. Although numerous point mutations were characterized in 131 polymerase chain reaction-generated clones of SIVmac gag, only four mutations within the gag CTL epitope-coding region of the genome were identified. Comparison of synonymous and nonsynonymous nucleotide substitutions in the regions encoding peptide 11C (p11C) and the flanking gag protein indicated a lack of selective pressure for viral mutations in the CTL epitope coding region. Interestingly, a predominant gag mutant encoding a single amino acid change in p11C was found in a monkey which lost its CTL activity. However, even in this setting there was no evidence for selection of mutations in the CTL epitope coding region when compared with the flanking region. Furthermore, synthetic peptides corresponding to all naturally occurring variants in the gag epitope-coding region were recognized by cloned and bulk cultured effector cells of the infected monkeys with persistent CTL. These results indicate that SIVmac gag- and p11C-specific CTL do not select for mutations in the immunodominant epitope-coding region and that the naturally occurring mutants do not appear to escape CTL recognition.

Amino Acid Sequence↗

PubMed1989

Structural requirements for membrane assembly of proteins spanning the membrane several times.

We have investigated the structural requirements for the biogenesis of proteins spanning the membrane several times. Proteins containing various combinations of topological signals (signal anchor and stop transfer sequences) were synthesized in a cell-free translation system and their membrane topology was determined. Proteins spanning the membrane twice were obtained when a signal anchor sequence was followed by either a stop transfer sequence or a second signal anchor sequence. Thus, a signal anchor sequence in the second position can function as a stop transfer sequence, spanning the membrane in the opposite orientation to that of the first signal anchor sequence. A signal anchor sequence in the third position was able to insert amino acid sequences located COOH terminal to it. We conclude that proteins spanning the membrane several times can be generated by stringing together signal anchor and stop transfer sequences. However, not all proteins with three topological signals were found to span the membrane three times. A certain segment located between the first and second topological signal could prevent stable membrane integration of a third signal anchor segment.

Cell Membrane↗

PubMed1987

DNA sequence analysis of host range mutants of the promiscuous IncP-1 plasmids R18 and R68 with Tn7 insertions in oriV.

Transposon Tn7 insertions in the origin of vegetative replication (oriV) result in host range mutants of the promiscuous IncP-1 plasmids R18 and R68 which affect plasmid replication in Escherichia coli but not in Pseudomonas aeruginosa. The sites of these insertions have been analyzed by DNA sequence analysis. In two mutants, the insertions generated direct duplications of 5'GTATT3' at the target site which included the first base at the 5' end of the fourth 17-bp direct repeat in oriV. In a third mutant the duplication of 5'GACAC3' also involved the same direct repeat also at the 5' end but contiguous with the previous duplication. DNA sequence analysis of another Tn7-induced host range mutant of R18, characterized by reduced conjugational transmissibility into P. stutzeri while retaining normal transmissibility within P. aeruginosa, showed that the insertion generated a 474-bp deletion which brought the insertion 20 bp 5' to the 17-bp direct repeat between oriV and the oxytetracycline hydrochloride-resistant gene. The analysis of the DNA sequence data at the site of the Tn7 insertions shows that particular segments of the DNA sequence in oriV are differentially required for the replication of these plasmids in different bacterial hosts and thus of importance to the promiscuity of these plasmids.

Base Sequence↗

PubMed1990

Cloning and sequencing of cDNAs coding for the human intra-acrosomal antigen SP-10.

cDNAs coding for the intra-acrosomal protein SP-10 were cloned and characterized as a first step in understanding the expression of this antigen during spermatogenesis. Three overlapping SP-10-specific cDNAs were isolated from a human testes cDNA expression library. These cDNAs hybridized to a 1.35-kb mRNA that was present in human testes but was not found in liver or placenta. Complete sequencing of these cDNAs, designated SP-10-5, SP-10-8, and SP-10-10, produced an 1117-bp sequence containing a 265-amino acid-coding region for the SP-10 protein. Hydrophobicity plots generated from the deduced amino acid sequence showed a very hydrophobic amino terminus characteristic of a signal peptide. Sequence data showed that three different amino acid repeats occurred a total of 16 times in the central third of the SP-10 protein. Interestingly, cDNA SP-10-10 has an internal 57-base pair (19 amino acids) in-frame deletion that is not present in SP-10-5, suggesting that alternative splicing generates more than one SP-10 mRNA. The SP-10 protein appears to be a unique acrosomal protein, based on previous immunohistological data and the observation that SP-10 cDNA sequences did not show any significant homology to other sequences found in the Genbank, National Biomedical Research Foundation, or Swiss sequence banks. A recombinant SP-10 fusion protein was produced in an Escherichia coli expression vector and used to generate a polyclonal antiserum. This antiserum stained the acrosomal cap in situ and reacted with a similar set of peptides on Western blots as did a monoclonal antibody to SP-10.

Acrosome↗

PubMed1991

Localization of the human complement component C3 binding site on the IgG heavy chain.

The location of the covalent binding site of the third component of complement (C3) on the IgG heavy chain was determined by sequence analysis of peptides generated by cyanogen bromide digestion of C3-IgG adducts. Activation of the alternative pathway by incubation of heat-aggregated human IgG1 with fresh normal human plasma formed covalent adducts of C3b-IgG. CNBr peptides of these adducts were transferred to a polyvinylidene difluoride membrane, and amino-terminal sequences were determined. A 40-kDa dipeptide containing the covalent bond was identified by labeling the free thiol group (generated during activation of the internal thioester of C3b) with iodo[1-14C]acetamide and analyzed by amino acid sequencing. The resulting double sequence suggested an adduct with NH2 termini at residue 938 (pro-C3 numbering) of C3 (75 residues NH2-terminal to the thioester) and residue 84 in the variable region of the IgG heavy chain. These results combined with results from hydroxylamine treatment (splits ester linkage between C3b and IgG) imply that this adduct peptide consists of a 22-kDa C3 fragment and an 18-kDa IgG fragment. Therefore, C3 binds covalently within the region extending from the last 20 residues of the variable region through the first 20 residues of CH2.

Amino Acid Sequence↗

PubMed1992

A general strategy for random insertion and substitution mutagenesis: substoichiometric coupling of trinucleotide phosphoramidites.

Results from a number of recent studies suggest that amino acid insertion mutations may provide an important alternative to substitution mutations for modifying protein structures and functional activities. To facilitate the use of single-amino acid insertions, we have developed a general strategy for inducing random, in-phase codon insertions across a defined segment of a cloned gene. In brief, a mixture of blocked and protected trinucleotide phosphoramidites is coupled at substoichiometric levels after every third monomer coupling on a conventional solid-state synthesizer. From the heterogeneous mixture of oligonucleotide sequences thus generated, those oligonucleotides that have acquired a single additional codon are purified by urea/PAGE. By using equimolar amounts of GCT and GGT trinucleotides in the oligonucleotide synthesis plus standard oligonucleotide-directed mutagenesis techniques, we have induced as many as 13 different single alanine and glycine insertion mutations into the gene for staphylococcal nuclease in one experiment. On replacement of the 5'-dimethoxytrityl blocking group on the trinucleotide phosphoramidite with an acid-stable blocking group, such as levulinate or fluoren-9-ylmethoxycarbonyl (Fmoc), this same strategy of substoichiometric couplings at codon boundaries should permit the synthesis of complex pools of oligonucleotides for the introduction, with constant efficiency, of every type of amino acid substitution at each codon across a gene segment.

Base Sequence↗

PubMedDate not supplied

Plasmid-mediated resistance to third-generation cephalosporins caused by point mutations in TEM-type penicillinase genes.

Infections due to strains of Klebsiella pneumoniae, Escherichia coli, and Citrobacter freundii resistant to third-generation cephalosporins have been observed recently in France and the Federal Republic of Germany. This resistance phenotype is due to the production of new plasmid-mediated, broad-substrate-range beta-lactamases designated TEM-3 to TEM-7. DNA-DNA hybridization analysis with a probe specific for TEM-1 indicated that the corresponding genes blaT-3 to blaT-7 were variants of the structural genes for TEM-type beta-lactamases. In the present studies, a 2.5-kilobase BamHI plasmid DNA fragment encoding TEM-3 was cloned in E. coli, and the entire nucleotide sequence of blaT-3 was determined. The deduced amino acid sequence of TEM-3 differed in two positions from that of the TEM-2 enzyme: lysine (TEM-3) was substituted for glutamic acid (TEM-2) at residue 104 and serine (TEM-3) for glycine (TEM-2) at residue 238 in the numbering system of Ambler. Spontaneous mutants of TEM penicillinases with increased activity against third-generation cephalosporins were obtained in vitro by selection on cefotaxime or ceftazidime. It therefore appears that mutations in TEM-type beta-lactamases contribute to resistance to new-generation cephalosporins.

Amino Acid Sequence↗

PubMed2025

Exome sequencing identifies a homozygous splice site variant in RP1 as the underlying cause of autosomal recessive retinitis pigmentosa in a Pakistani family.

BACKGROUND: Mutations in RP1 gene are the third leading cause of inherited retinal dystrophies (IRDs) in Pakistani families. PATIENTS: A two-generation consanguineous Pakistani family underwent both clinical and genetic analyses. Clinical examinations included visual acuity test, visual field, fundoscopy, and ocular coherence tomography (OCT). Whole exome sequencing (WES) was performed on the proband's DNA, and Sanger sequencing was performed to validate the WES findings. Splicing prediction tools such as Human Splicing Finder (HSF), NNSplice predictor, SpliceAI, MaxENTScan, and SpliceRover were used. RESULTS: A nuclear family of seven children, comprising five affected individuals (four males and one female) and two healthy siblings, was recruited from northwestern Pakistan. The proband was a 49-years old male who was presented with complaints of decreased visual acuity and night blindness since early childhood. Upon clinical evaluation, the proband appeared to have severely reduced visual acuity of hand movement (HM), bilateral visual field constriction, a waxy pale disc with vascular attenuation, pigmentary bone spicules at the periphery associated with chorioretinal degeneration, diffuse macular atrophy, and horizontal nystagmus in both of his eyes. Exome sequencing (ES) in the proband identified a homozygous splice site variant (NM_006269.2: c.615 + 1G > A) in RP1 gene. In-silico analysis, genotype-phenotype co-segregation study, and literature survey strongly supported the causality of the detected variant. CONCLUSIONS: We report a previously known pathogenic splice site variant of RP1 as the underlying cause of early-onset autosomal recessive retinitis pigmentosa (arRP) in a Pakistani family. We contemplate that the detected allele might constitute a mutational hotspot in RP1.

Humans↗

PubMed1990

Multiecho multimoment refocussing of motion in magnetic resonance imaging: MEM-MO-RE.

Gradient moment nulling techniques for refocussing of spin dephasing resulting from movement during application of magnetic resonance imaging gradients have gained widespread application. These techniques offer advantages over conventional imaging gradients by reducing motion artifacts due to intraview motion, and by recovering signal lost from spin dephasing. This paper presents a simple technique for designing multiecho imaging gradient waveforms that refocus dephasing from the interaction of imaging gradients and multiple derivatives of position. Multiple moments will be compensated at each echo. The method described relies on the fact that the calculation of time moments for nulled moment gradient waveforms is independent of the time origin chosen. Therefore, waveforms used to generate the second echo image for multiple echo sequences with echo times given by TEn = TE1 + (n - 1) * (TE2 - TE1) may also be used for generation of the third and additional echo images. All echoes will refocus the same derivatives of position. Multiecho, multimoment refocussing (MEM-MO-RE) images through the liver in a patient with ampullary adenocarcinoma metastatic to the liver demonstrate the application of the method in clinical scanning.

Adenocarcinoma↗

PubMed1989

Evolutionary pathways of the calcitonin (CALC) genes.

Recombinant DNA techniques have made it possible to establish the structure of various genes encoding polypeptide hormones. Comparison of nucleotide sequences of the calcitonin (CALC) genes in man has revealed surprising similarities and variations. These findings and the homologies among the sequences in different species offered an opportunity for speculation about relationships between these genes and about their evolutionary origin. The first gene (CALC-I) directing the synthesis of calcitonin (CT) or CT gene-related peptide (CGRP) comprises six exons and gives rise to two mRNAs by an alternative RNA-processing mechanism. The homology between CGRP and CT reflects their common origin. The human genome contains a second gene (CALC-II) that is structurally related to the CALC-I gene. The CALC-II RNA transcripts do not appear to be differentially processed, as only preproCGRP-II mRNA and not preproCT-II is detected. The first and second CT/CGRP genes probably have evolved from a common ancestor gene early in evolution. Meanwhile, a third genomic locus containing nucleotide sequences highly homologous to exons 2 and 3 of both CALC genes was detected and probably generated by duplication of a part of CALC-II. This locus is not likely to encode a CT- or CGRP-related polypeptide hormone. The CALC genes and this last (pseudo) gene are located on the short arm of chromosome 11. Recently, islet- or insulinoma-amyloid polypeptide (IAPP) was isolated as a major constituent of amyloid present in human insulinoma and in pancreatic islet amyloid in noninsulin-dependent diabetes mellitus. IAPP shows 46% amino acid sequence homology with human CGRP-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid↗