Biomedical subjects

D Ruezinsky

Publications and source records attributed to D Ruezinsky.

5 recordsLinked to original sources

PubMed1994

Displacement of an E-box-binding repressor by basic helix-loop-helix proteins: implications for B-cell specificity of the immunoglobulin heavy-chain enhancer.

The activity of the immunoglobulin heavy-chain (IgH) enhancer is restricted to B cells, although it binds both B-cell-restricted and ubiquitous transcription factors. Activation of the enhancer in non-B cells upon overexpression of the basic helix-loop-helix (bHLH) protein E2A appears to be mediated not only by the binding of E2A to its cognate E box but also by the resulting displacement of a repressor from that same site. We have identified a "two-handed" zinc finger protein, denoted ZEB, the DNA-binding specificity of which mimics that of the cellular repressor. By employing a derivative E box that binds ZEB but not E2A, we have shown that the repressor is active in B cells and the IgH enhancer is silenced in the absence of binding competition by bHLH proteins. Hence, we propose that a necessary prerequisite of enhancer activity is the B-cell-specific displacement of a ZEB-like repressor by bHLH proteins.

Amino Acid Sequence↗

PubMed1991

Modulation of the IgH enhancer's cell type specificity through a genetic switch.

Using defined regions of the immunoglobulin heavy-chain enhancer linked to minimal promoters and cDNAs that encode the two helix-loop-helix transcription factors ITF-1 and TFE3, we demonstrate that activity of an otherwise repressed enhancer can be stimulated in nonlymphoid cells. Repression in non-B cells is mediated by the microE5 motif. Derepression occurs at two levels. First, overexpression of ITF-1, and E12/E47-related protein that binds the microE5 motif, leads to transcriptional activation itself. Second, binding of ITF-1 physically displaces a repressor that normally blocks the stimulatory activity of TFE3, which binds the neighboring microE3 motif. TFE3 can only stimulate enhancer activity in the presence of ITF-1 or in the absence of a microE5 motif. Hence, one component of the enhancer's cell type specificity can be artificially modulated through a "genetic switch" in which activity is dictated by the relative levels of ITF-1 and a competing repressor.

Base Sequence↗

PubMed1986

Functional analysis of the murine IgH enhancer: evidence for negative control of cell-type specificity.

We have carried out a mutational analysis of the mouse IgH enhancer. Consistent with previous reports, deletions extending from either the 5' side or the 3' side of the enhancer fail to reveal distinct boundaries which define enhancer function in lymphoid cells. Interestingly, internal point mutations and deletions within the "enhancer core" regions fail to identify any necessary functional role for these conserved elements. When tested in CV1 cells, which do not normally respond to the IgH enhancer, certain deletions exhibit significant enhancer activity. We take these findings to indicate that the functional domains of the IgH enhancer are complex and that cell type specificity is defined in part by negative factors present in non-lymphoid cells.

Animals↗

PubMed1985

Inter- and intraclonal diversity in the antibody response to influenza hemagglutinin.

This study focuses on 10 BALB/c anti-influenza virus (A/PR/8/34) hemagglutinin antibodies that have light chains encoded by the same variable region kappa chain (V kappa) gene, V kappa 21C. A comparison of antibodies from lymphocytes of independent origin reveals the contribution of germline diversity (combinatorial joining and association) to this response. Although combinatorial joining and association contribute to sequence diversity, they appear to have little effect on the fine specificity of these antibodies. Somatic mutation, in addition to contributing to the sequence diversity of these antibodies, creates differences in their fine specificity. The extent of mutation and its effect on fine specificity can be seen by comparing antibodies of lymphocytes from the same clone. These intraclonal comparisons also indicate that somatic mutation is an ongoing process occurring at a high rate (estimated to be at least 10(-3) mutations per base pair per division) in the expressed V region heavy chain (VH) and V kappa genes. Furthermore, both the nature and distribution of these mutations suggest that amino acid replacement mutations in the light but not the heavy chain are selected for by antigen.

Animals↗

PubMed1984

Temperature-sensitive lethal mutations on yeast chromosome I appear to define only a small number of genes.

A method was developed for isolating large numbers of mutations on chromosome I of the yeast Saccharomyces cerevisiae. A strain monosomic for chromosome I (i.e., haploid for chromosome I and diploid for all other chromosomes) was mutagenized with either ethyl methanesulfonate or N-methyl-N'-nitro-N-nitrosoguanidine and screened for temperature-sensitive (Ts-) mutants capable of growth on rich, glucose-containing medium at 25 degrees but not at 37 degrees. Recessive mutations induced on chromosome I are expressed whereas those on the diploid chromosomes are usually not expressed because of the presence of wild-type alleles on the homologous chromosomes. Dominant ts mutations on all chromosomes should also be expressed, but these appeared rarely.--Of the 41 ts mutations analyzed, 32 mapped on chromosome I. These 32 mutations fell into only three complementation groups, which proved to be the previously described genes CDC15, CDC24 and PYK1 (or CDC19). We recovered 16 or 17 independent mutations in CDC15, 12 independent mutations in CDC24 and three independent mutations in PYK1. A fourth gene on chromosome I, MAK16, is known to be capable of giving rise to a ts-lethal allele, but we recovered no mutations in this gene. The remaining nine mutations isolated using the monosomic strain appeared not to map on chromosome I and were apparently expressed in the original mutants because they had become homozygous or hemizygous by mitotic recombination or chromosome loss.--The available information about the size of chromosome I suggests that it should contain approximately 60-100 genes. However, our isolation in the monosomic strain of multiple, independent alleles of just three genes suggests that only a small proportion of the genes on chromosome I is easily mutable to give a Ts--lethal phenotype.--During these studies, we located CDC24 on chromosome I and determined that it is centromere distal to PYK1 on the left arm of the chromosome.

Chromosome Mapping↗