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PubMed2001

Binding of serum response factor to CArG box sequences is necessary but not sufficient to restrict gene expression to arterial smooth muscle cells.

Serum response factor (SRF) plays an important role in regulating smooth muscle cell (SMC) development and differentiation. To understand the molecular mechanisms underlying the activity of SRF in SMCs, the two CArG box-containing elements in the arterial SMC-specific SM22alpha promoter, SME-1 and SME-4, were functionally and biochemically characterized. Mutations that abolish binding of SRF to the SM22alpha promoter totally abolish promoter activity in transgenic mice. Moreover, a multimerized copy of either SME-1 or SME-4 subcloned 5' of the minimal SM22alpha promoter (base pairs -90 to +41) is necessary and sufficient to restrict transgene expression to arterial SMCs in transgenic mice. In contrast, a multimerized copy of the c-fos SRE is totally inactive in arterial SMCs and substitution of the c-fos SRE for the CArG motifs within the SM22alpha promoter inactivates the 441-base pair SM22alpha promoter in transgenic mice. Deletion analysis revealed that the SME-4 CArG box alone is insufficient to activate transcription in SMCs and additional 5'-flanking nucleotides are required. Nuclear protein binding assays revealed that SME-4 binds SRF, YY1, and four additional SMC nuclear proteins. Taken together, these data demonstrate that binding of SRF to specific CArG boxes is necessary, but not sufficient, to restrict transgene expression to SMCs in vivo.

3' Untranslated Regions↗

PubMed2001

An E-box motif residing in the exon/intron 1 junction regulates both transcriptional activation and splicing of the human norepinephrine transporter gene.

The norepinephrine transporter (NET) is responsible for the rapid NaCl-dependent uptake of norepinephrine into presynaptic noradrenergic nerve endings. Recently, we have characterized the structural organization of the 5' upstream promoter region of the human NET (hNET) gene. A new intron of 476 base pairs was found in the middle of the 5'-untranslated leader sequence and was shown to robustly enhance the promoter activity. Here, we show that the first hNET intron enhances both the homologous hNET and the heterologous thymidine kinase promoter activities in an orientation- and position-dependent manner. The first hNET intron exhibited a similar promoter-enhancing effect in both SK-N-BE(2)C (NET-positive) and HeLa (NET-negative) cell lines, showing that its function is not cell-specific. Transient transfection assays of a series of deletional constructs show that the first hNET intron contains subdomains with either positive or negative regulatory functions. Furthermore, DNase I footprinting analysis demonstrated that the 5' side of the intron, encompassing the splice donor site, is prominently protected by nuclear proteins isolated from both SK-N-BE(2)C and HeLa cells. The protected nucleotide sequence contains a consensus E-box motif, known to regulate diverse eukaryotic genes, which overlaps with the splice donor site of the first intron. We demonstrate that two basic helix-loop-helix proteins, upstream stimulatory factors 1 and 2, are major proteins interacting at this site and that the E-box is at least in part responsible for the promoter-enhancing activity of the first intron. Furthermore, site-directed mutagenesis of the splice donor site of the first intron affects both correct splicing and transcriptional activity. Taken together, our results indicate that a cis-element residing at the first exon/intron junction, encompassing an E-box motif, has a unique dual role in basal transcriptional activation and splicing of hNET mRNA.

Base Sequence↗

PubMed2001

Critical roles of a cyclic AMP responsive element and an E-box in regulation of mouse renin gene expression.

Mouse As4.1 cells, obtained after transgene-targeted oncogenesis to induce neoplasia in renal renin expressing cells, express high levels of renin mRNA from their endogenous Ren-1(c) gene. We have previously identified a 242-base pair enhancer (coordinates -2866 to -2625 relative to the CAP site) upstream of the mouse Ren-1(c) gene. This enhancer, in combination with the proximal promoter (-117 to +6), activates transcription nearly 2 orders of magnitude in an orientation independent fashion. To further delimit sequences necessary for transcriptional activation, renin promoter-luciferase reporter gene constructs containing selected regions of the Ren-1(c) enhancer were analyzed after transfection into As4.1 cells. These results demonstrate that several regions are required for full enhancer activity. Sequences from -2699 to -2672, which are critical for the enhancer activity, contain a cyclic AMP responsive element (CRE) and an E-box. Electrophoretic mobility shift assays demonstrated that transcription factors CREB/CREM and USF1/USF2 in As4.1 cell nuclear extracts bind to oligonucleotides containing the Ren-1(c) CRE and E-box, respectively. These two elements are capable of synergistically activating transcription from the Ren-1(c) promoter. Moreover, mutation of either the CRE or E-box results in almost complete loss of enhancer activity, suggesting the critical roles these two elements play in regulating mouse Ren-1(c) gene expression. Although the Ren-1(c) gene contains a CRE, its expression is not induced by cAMP in As4.1 cells. This appears to reflect constitutive activation of protein kinase A in As4.1 cells since treatment with the protein kinase A inhibitor, H-89, caused a significant reduction in Ren-1(c) gene expression and this reduction is mediated through the CRE at -2699 to -2688.

Animals↗

PubMed2001

A novel brain-specific box C/D small nucleolar RNA processed from tandemly repeated introns of a noncoding RNA gene in rats.

Antisense box C/D small nucleolar RNAs (snoRNAs) guide the 2'-O-ribose methylations of eukaryotic rRNAs and small nuclear RNAs (snRNAs) through formation of a specific base pairing at each RNA methylation site. By analysis of a box C/D snoRNA cDNA library constructed from rat brain RNAs, we have identified a novel box C/D snoRNA, RBII-36, which is devoid of complementarity to rRNA or an snRNA and exhibits a brain-specific expression pattern. It is uniformly expressed in all major areas of adult rat brain (except for choroid plexus) and throughout rat brain ontogeny but exclusively detected in neurons in which it exhibits a nucleolar localization. In vertebrates, known methylation guide snoRNAs are intron-encoded and processed from transcripts of housekeeping genes. In contrast, RBII-36 snoRNA is intron-encoded in a gene preferentially expressed in the rat central nervous system and not in proliferating cells. Remarkably, this host gene, which encodes a previously reported noncoding RNA, Bsr, spans tandemly repeated 0.9-kilobase units including the snoRNA-containing intron. The novel brain-specific snoRNA appears to result not only from processing of the debranched lariat but also from endonucleolytic cleavages of unspliced Bsr RNA (i.e. an alternative splicing-independent pathway unreported so far for mammalian intronic snoRNAs). Sequences homologous to RBII-36 snoRNA were exclusively detected in the Rattus genus of rodents, suggesting a very recent origin of this brain-specific snoRNA.

Animals↗

PubMed2001

The Cold Box stem-loop proximal to the 5'-end of the Escherichia coli cspA gene stabilizes its mRNA at low temperature.

The 5'-end region of cspA mRNA contains a Cold Box sequence conserved among several cold-shock mRNAs. This region forms a stable stem-loop structure followed by an AU-rich sequence. Here we show that the Cold Box region is essential for the normal scale of cspA mRNA induction after cold shock because a deletion of the stem-loop significantly destabilizes the mRNA and reduces the cold shock-induced cspA mRNA amount by approximately 50%. The AU-rich track, however, slightly destabilizes the mRNA. The integrity of the stem is essential for the stabilizing function, whereas that of the loop sequence is less important. Overexpression of a mutant cspA mRNA devoid of both the AUG initiation codon and the coding sequence results in a severe growth inhibition at low temperature along with a derepression of the chromosomal cspA expression. Furthermore, the overexpressed RNA is stably associated with the 30 S and 70 S ribosomes. Our results demonstrate that the AUG initiation codon and the coding region containing the downstream box are not required for cspA mRNA to bind ribosomes and that the 5'-untranslated region by itself has a remarkable affinity to ribosomes at low temperature.

5' Untranslated Regions↗

PubMed2002

Identification of sterol-independent regulatory elements in the human ATP-binding cassette transporter A1 promoter: role of Sp1/3, E-box binding factors, and an oncostatin M-responsive element.

The ATP-binding cassette transporter A1 (ABCA1) shows a differentiation-, cAMP-, and sterol-dependent up-regulation in human monocytes. As part of an ongoing study, we investigated the proximal promoter regions that are highly conserved between the human and murine ABCA1 genes. Using reporter gene assays, we show here that a TATA box 24 bp upstream of the transcription initiation site is essential for promoter activity in RAW 264.7 and HepG2 cells, whereas further enhancement of transcriptional activity is mediated by the -175 bp promoter region. Gel shift assays revealed in vitro binding of Sp1 to a -91 GnC motif as well as binding of Sp1 and Sp3 to a -157 GnC promoter region. In co-transfection experiments using Drosophila S2 cells, we demonstrate that Sp3 competes with Sp1 for binding to the -157 GnC motif and acts as a repressor. On the other hand, overexpression of Sp1 increased ABCA1 mRNA expression in HeLa cells and enhanced cellular cholesterol and phospholipid efflux in RAW 246.7 macrophages. We also show here that the conserved E-box at position -140 binds upstream stimulatory factors 1 and 2 and hepatic nuclear factor 1alpha and that mutagenesis of the E-box enhanced constitutive ABCA1 expression in RAW 264.7 cells, implying a role for this element in silencing ABCA1 expression. Besides the functional importance for basal gene expression, we have identified that the core promoter region (-175 to +224) is also responsible for the induction of ABCA1 by the cytokine oncostatin M, resulting in a rapid increase in ABCA1 mRNA levels in HepG2 cells. Interestingly, this oncostatin M-induced expression is not dependent on the currently known sequence motifs in the ABCA1 promoter. In conclusion, a functional complex of cis-elements within the proximal human ABCA1 promoter associated with the transcription factors Sp1/3, upstream stimulatory factors 1 and 2, and hepatic nuclear factor 1alpha has been characterized, which allows a subtle tissue-specific regulation of ABCA1 gene expression.

ATP-Binding Cassette Transporters↗

PubMed2002

Stra13 homodimers repress transcription through class B E-box elements.

A mammalian basic helix-loop-helix protein known variably as Stra13, Sharp2, and Dec1 has been implicated in cell activation, proliferation, and differentiation. Indeed, Stra13 null mice develop age-induced autoimmunity as a result of impaired T-lymphocyte activation, leading ultimately to the accumulation of autoreactive T-cells and B-cells. Stra13 is expressed in embryonic as well as adult tissues derived from neuroectoderm, mesoderm, and endoderm and has been associated with response to hypoxia, suggesting a complex role for this protein and the highly related Sharp1/Dec2 protein in homeostatic regulation. Whereas Stra13 is known to regulate many important cellular functions and is known to cross-regulate biological responses to other basic helix-loop-helix containing transcription factors, including c-Myc and USF, it is unclear if this protein binds directly to DNA. Indeed, the basic domain of Stra13 contains a proline residue at an unprecedented position. Herein, we have determined that Stra13 binds with high affinity to CACGTG class B E-box elements as a homodimer with preference for elements preceded by T and/or followed by A residues. In addition, transient transfection experiments reveal that Stra13 represses transcription when bound to these and related sites. Our data suggest that Stra13 regulates cellular functions through antagonism of E-box activator proteins and also through active repression from E-box elements.

Animals↗

PubMed2002

A spindle checkpoint arrest and a cytokinesis failure by the dominant-negative polo-box domain of Plk1 in U-2 OS cells.

Polo kinases play critical roles for proper M-phase progression. They are characterized by the presence of two regions of homology in the C-terminal non-catalytic domain, termed polo-box 1 (PB1) and polo-box 2 (PB2). Here we demonstrate that both PB1 and PB2 are required for targeting the catalytic activity of Plk1 to centrosomes, midbody, and kinetochores. Expression of either kinase-inactive PLK1/K82M or the C-terminal plk1 Delta N induced a pre-anaphase arrest with elevated Cdc2 and Plk1 activity. Prophase-arrested cells exhibited randomly oriented spindle structures, whereas metaphase cells exhibited aberrant bipolar spindles with Mad2 localization at kinetochores of misaligned chromosomes. Microtubule nucleation activity of centrosomes was not compromised. In vivo time-lapse studies revealed that expression of plk1 Delta N resulted in repeated cycles of bipolar spindle formation and disruption, suggestive of a defect in spindle stability. A prolonged arrest frequently led to the generation of micronucleated cells in the absence of sisterchromatid separation and centrosome duplication, indicating that micronucleation is not a result of accumulated cytokinesis failures. Interestingly, bypass of the mitotic arrest by dominant-negative spindle checkpoint components led to a failure in completion of cytokinesis. We propose that, in mammalian cells, the polo-box-dependent Plk1 activity is required for proper metaphase/anaphase transition and for cytokinesis.

Anaphase↗

PubMed2003

Identification of a novel Krüppel-associated box domain protein, Krim-1, that interacts with c-Myc and inhibits its oncogenic activity.

We have used the Ras recruitment system to screen for proteins that interact with the N-terminally located transactivation domain of c-Myc. The Ras recruitment system is based on the activation of the mitogenic RAS signaling pathway in yeast by the mammalian GTPase Ha-Ras. This screen led to the identification of two novel nuclear proteins termed Krim-1A and Krim-1B that both contain an N-terminal KRAB box domain and 12 or 9 Krüppel C2H2 type zinc fingers at the C terminus, respectively. We found that sequences covering the Myc box II homology region are essential for the interaction with the Krim-1 proteins and that the second N-terminal zinc finger of Krim-1 is essential for Myc binding. Both Krim-1A and -B genes appear to be expressed ubiquitously with highest levels in spleen and lymph nodes. In particular, Krim-1B and, to a lesser extent, Krim-1A are able to decrease E-box-dependent transcriptional transactivation by c-Myc-Max complexes and also the ability of Myc to malignantly transform primary rat embryo fibroblasts, which is consistent with the functional repressive properties of their KRAB domains. The transcriptional corepressor Tif-1beta is a binding partner for Krim-1 and stabilizes the protein. Our findings suggest that Myc-mediated functions can be negatively regulated by Krim-1, potentially in a complex with Tif-1beta.

3T3 Cells↗

PubMed2002

Regulation of lipocalin-type prostaglandin D synthase gene expression by Hes-1 through E-box and interleukin-1 beta via two NF-kappa B elements in rat leptomeningeal cells.

The promoter function of the rat lipocalin-type prostaglandin D synthase (L-PGDS) gene was characterized in primary cultures of leptomeningeal cells prepared from the neonatal rat brain. Luciferase reporter assays with deletion and site-directed mutation of the promoter region (-1250 to +77) showed that an AP-2 element at -109 was required for activation and an E-box at +57, for repression. Binding of nuclear factors to each of these cis-elements was demonstrated by an electrophoretic mobility shift assay. Several components of the Notch-Hes signaling pathway, Jagged, Notch1, Notch3, and Hes-1, were expressed in the leptomeningeal cells. Human Hes-1 co-expressed in the leptomeningeal cells bound to the E-box of the rat L-PGDS gene, and repressed the promoter activity of the rat L-PGDS gene in a dose-dependent manner. The L-PGDS gene expression was up-regulated slowly by interleukin-1 beta to the maximum level at 24 h. The reporter assay with deletion and mutation revealed that two NF-kappa B elements at -1106 and -291 were essential for this up-regulation. Binding of two NF-kappa B subunits, p65 and c-Rel, to these two NF-kappa B elements occurred after the interleukin-1 beta treatment. Therefore, the L-PGDS gene is the first gene identified as the target for the Notch-Hes signal through the E-box among a variety of genes involved in the prostanoid biosynthesis, classified to the lipocalin family, and expressed in the leptomeninges. Moreover, the L-PGDS gene is a unique gene that is activated slowly by the NF-kappa B system.

Animals↗

PubMed2003

Structural analysis of the DNA-binding domain of the Erwinia amylovora RcsB protein and its interaction with the RcsAB box.

The transcriptional regulator RcsB interacts with other coactivators to control the expression of biosynthetic operons in enterobacteria. While in a heterodimer complex with the regulator RcsA the RcsAB box consensus is recognized, DNA binding sites for RcsB without RcsA have also been identified. The conformation of RcsB might therefore be modulated upon interaction with various coactivators, resulting in the recognition of different DNA targets. We report the solution structure of the C-terminal DNA-binding domain of the RcsB protein from Erwinia amylovora spanning amino acid residues 129-215 solved by heteronuclear magnetic resonance (NMR) spectroscopy. The C-terminal domain is composed of four alpha-helices where two central helices form a helix-turn-helix motif similar to the structures of the regulatory proteins GerE, NarL, and TraR. Amino acid residues involved in the RcsA independent DNA binding of RcsB were identified by titration studies with a RcsAB box consensus fragment. Data obtained from NMR spectroscopy together with surface plasmon resonance measurements demonstrate that the RcsAB box is specifically recognized by the RcsAB heterodimer as well as by RcsB alone. However, the binding constant of RcsB alone at target promoters from Escherichia coli, E. amylovora, and Pantoea stewartii was approximately 1 order of magnitude higher compared with that of the RcsAB heterodimer. We present evidence that the obvious role of RcsA is not to alter the DNA binding specificity of RcsB but to stabilize RcsB-DNA complexes.

Amino Acid Motifs↗

PubMed2003

Plakoglobin is O-glycosylated close to the N-terminal destruction box.

Plakoglobin provides a key linkage in protein chains that connect desmosomal and classical cadherins to the cytoskeleton. It is also present in a significant cytosolic pool that has the capacity to impact on canonical Wnt signaling by competing for interaction with partner proteins of beta-catenin. The closely related protein, beta-catenin, is rapidly targeted for proteasomal degradation by phosphorylation of a "destruction box" within the N-terminal domain. Inhibition of this process forms the basis of Wnt signaling. This destruction box is also found in the N-terminal domain of plakoglobin. We report that plakoglobin is modified by the addition of O-GlcNAc at a single site in close proximity to the destruction box. O-GlcNAc modification has been proposed to counteract phosphorylation, provide protection from proteasomal degradation, mediate signal transduction, silence transcription, and regulate multimolecular protein assembly. This finding has potential implications for understanding the roles of plakoglobin.

Amino Acid Sequence↗

PubMed2004

Stability of homologue of Slimb F-box protein is regulated by availability of its substrate.

The homologue of Slimb (HOS) F-box protein is a receptor of the Skp1-Cullin1-F-box protein (SCF(HOS)) E3 ubiquitin ligase, which mediates ubiquitination and degradation of beta-catenin and the inhibitor of NFkappaB, IkappaB. We found that HOS itself is an unstable protein that undergoes ubiquitination and degradation in a 26 S proteasome-dependent manner. A HOS mutant lacking the F-box that is deficient in binding to the core SCF components underwent ubiquitination less efficiently and was more stable than the wild type protein. Furthermore, ubiquitination and degradation of HOS was impaired in ts41 cells, in which the activities of Cullin-based ligases were decreased because the NEDD8 pathway was abrogated. Whereas HOS was directly ubiquitinated within the SCF(HOS) complex in vitro, the addition of phosphorylated IkappaBalpha inhibited this ubiquitination. Increasing cellular levels of HOS substrate (phosphorylated IkappaBalpha) by activating IkappaB kinase inhibited HOS ubiquitination and led to stabilization of HOS, indicating that interaction between HOS and its substrate might protect HOS from proteolysis. Taken together, our data suggest that proteolysis of HOS depends on its interaction with active components of the SCF complex and that HOS stability is regulated by a bound substrate. These findings may define a mechanism for maintaining activities of specific SCF complexes based on availability of a particular substrate.

Base Sequence↗

PubMed2004

The box VII motif of Escherichia coli DnaA protein is required for DnaA oligomerization at the E. coli replication origin.

Escherichia coli DnaA protein initiates DNA replication from the chromosomal origin, oriC, and regulates the frequency of this process. Structure-function studies indicate that the replication initiator comprises four domains. Based on the structural similarity of Aquifex aeolicus DnaA to other AAA+ proteins that are oligomeric, it was proposed that Domain III functions in oligomerization at oriC (Erzberger, J. P., Pirruccello, M. M., and Berger, J. M. (2002) EMBO J. 21, 4763-4773). Because the Box VII motif within Domain III is conserved among DnaA homologues and may function in oligomerization, we substituted conserved Box VII amino acids of E. coli DnaA with alanine by site-directed mutagenesis to examine the role of this motif. All mutant proteins are inactive in initiation from oriC in vivo and in vitro, but they support RK2 plasmid DNA replication in vivo. Thus, RK2 requires only a subset of DnaA functions for plasmid DNA replication. Biochemical studies on a mutant DnaA carrying an alanine substitution at arginine 281 (R281A) in Box VII show that it is inactive in in vitro replication of an oriC plasmid, but this defect is not from the failure to bind to ATP, DnaB in the DnaB-DnaC complex, or oriC. Because the mutant DnaA is also active in the strand opening of oriC, whereas DnaB fails to bind to this unwound region, the open structure is insufficient by itself to load DnaB helicase. Our results show that the mutant fails to form a stable oligomeric DnaA-oriC complex, which is required for the loading of DnaB.

Adenosine Triphosphatases↗

PubMed2006

Solution structure and antiestrogenic activity of the unique C-terminal, NR-box motif-containing region of MTA1s.

Metastasis tumor-associated 1 short form (MTA1s) is a naturally occurring, alternatively spliced variant of MTA1 that functions as a repressor of estrogen receptor (ER) alpha transcriptional functions, at least in part by binding and sequestering ERalpha in the cytoplasm. A unique C-terminal 33-amino acid region containing a nuclear receptor (NR)-box motif (-LRILL-) mediates binding of MTA1s with ERalpha and is indispensable in this interaction. Here, we elucidated the solution structure of this 33-amino acid region by NMR spectroscopy. We found a predominance of the alpha-helical region toward the N-terminal region, which includes the NR-box motif. In silico docking and comparison studies showed similarities between the NR-box motif of MTA1s and a similar motif of coregulators, both in structure and mode of ERalpha binding. In MCF-7 breast cancer cells, the MTA1s peptide effectively repressed ERalpha transactivation function, as evidenced by the estrogen response element-luc assay and down-regulation of estrogen-induced genes. In mechanistic studies, we found that the antiestrogenic effects of the MTA1s peptide were due to its ability to compete with the coactivator recruitment to ERalpha. Furthermore, the peptide efficiently repressed estrogen-induced proliferation and anchorage-independent growth of MCF-7 cells. In addition, the MTA1s peptide blocked the progression of tumors formed by MCF-7 cells overexpressing an ERalpha coactivator in a xenograft-based assay. In brief, the characterization of structure and antiestrogenic activity of MTA1s peptide highlight its therapeutic potential.

Animals↗

PubMed1995

Development of factor-score-based models to explain and predict maximal box-lifting performance.

The objectives of the study were threefold: (1) to develop factor-score-based models to predict maximum mass on a box-lifting task using multiple regressions; (2) to compare predictive and explanatory powers of factor-score-based models to models derived from data-level variables; and (3) to apply these findings to ergonomic research and practical problem-solving situations. Forty-eight volunteers (25 women and 23 men) completed a maximal box-lifting task and a maximal isoinertial lifting test on an Incremental Lifting Machine (ILM). Dynamic data collected during isoinertial testing were summarized into 32 lift parameters, and then subjected to principal components analyses using the 'FACTOR PROCEDURE' from the Statistical Analysis System (SAS). Factor scores were calculated for each participant on each of the four factors comprising the final solution, and multiple regression equations for men, women and combined data were generated using the 'GENERAL LINEAR MODELS' procedure from SAS. Results revealed that prediction of box-lifting performance was optimized when regression equations were developed using numerous data-level variables as predictors, i.e., all 32 lift parameters and ILM mass. In comparison, explanation was enhanced but predictive capabilities were reduced when linear models were formed using ILM mass and the factor scores derived from analyses of isoinertial lifting. The use of variables loading on the factors gave slightly increased predictive power than did the factor-score-based models. Similar trends in predictive and explanatory powers appeared when the data were analysed according to gender. Ergonomic applications of factor-score-based models were discussed with regard to ongoing research as well as to practical problem-solving situations. It was concluded that the advantages and usefulness of factor-score-based models warranted their inclusion in future investigations of lifting performance.

Adult↗

PubMed1996

HMG box proteins interact with multiple tandemly repeated (GCC)n (GGC)m DNA sequences.

A number of tandemly repeated DNA sequences have the ability to form hairpin structures by forming non-standard base pairs. When (GCC)15 and (GGC)15 strands are annealed together, the expected duplex is the only product. However, when (GCC)15 is annealed with (GCC)10, depending on the relative concentrations, up to five complexes can be detected in native gels. Three of these species are susceptible to limited digestion by Exo VII, suggesting they are duplexes containing single stranded tails. The remaining two bands are resistant to the enzyme, and have low mobility on native gels, consistent with branched structures. The latter complexes bind HMG box proteins, members of a highly abundant class of non-histone proteins of the nucleus. These proteins, modeled in this study by the second box fragment from rat HMG1, HMGb, interact strongly with branched or chemically modified DNA, relative to normal duplexes. The expansion of triplet repeats in genomic DNA is associated with tumor formation as well with a variety of heritable neurologiocal disorders. It is our thesis that the stability of branched intermediate structures that arise in replication of these sequences and promote expansion can be influenced directly by the presence of two highly abundant proteins in the cell nucleus: the HMG box proteins, HMG1/2, and the histone H1, which associates with HMG1/2.

Bacterial Proteins↗

PubMedDate not supplied

Microclimates and energetics of free-living box turtles, Terrapene carolina, in South Carolina.

We measured microclimate, field metabolic rates (FMRs), water flux, and activity patterns of telemetered box turtles (Terrapene carolina) in South Carolina from September 1987 to October 1988. Turtles were inactive for most of the winter and were active only sporadically during the rest of the year. Using the doubly labeled water method, we found that water flux averaged 8.8, 18.9, and 26.4 mL kg(-1) d(-1) in winter, spring, and summer/fall, respectively. FMR for the same periods averaged 0.028, 0.065, and 0.124 mL CO(2) g(-1) h(-1). Differences in FMR among seasons were significant but not between sexes. Using operative temperatures, we predicted standard and maximum metabolic rates of turtles. In winter, FMR was elevated above standard metabolic rates and close to maximum metabolic rates, whereas in spring and summer/fall, FMR fell midway between standard and maximum metabolic rates. We used a model to predict metabolic rates, geographical distribution, and potential reproductive output of box turtles across latitudes in eastern North America. Low FMR and low annual reproductive output may allow box turtles to survive and flourish in unpredictable resource environments by minimizing costs and risks, thereby maintaining greater lifetime reproductive success.

Activity Cycles↗