Biomedical subjects

Irwin Davidson

Publications and source records attributed to Irwin Davidson.

21 records · Page 2Linked to original sources

PubMed2002

Distinct mutations in yeast TAF(II)25 differentially affect the composition of TFIID and SAGA complexes as well as global gene expression patterns.

The RNA polymerase II transcription factor TFIID, composed of the TATA-binding protein (TBP) and TBP-associated factors (TAF(II)s), nucleates preinitiation complex formation at protein-coding gene promoters. SAGA, a second TAF(II)-containing multiprotein complex, is involved in transcription regulation in Saccharomyces cerevisiae. One of the essential protein components common to SAGA and TFIID is yTAF(II)25. We define a minimal evolutionarily conserved 91-amino-acid region of TAF(II)25 containing a histone fold domain that is necessary and sufficient for growth in vivo. Different temperature-sensitive mutations of yTAF(II)25 or chimeras with the human homologue TAF(II)30 arrested cell growth at either the G(1) or G(2)/M cell cycle phase and displayed distinct phenotypic changes and gene expression patterns. Immunoprecipitation studies revealed that TAF(II)25 mutation-dependent gene expression and phenotypic changes correlated at least partially with the integrity of SAGA and TFIID. Genome-wide expression analysis revealed that the five TAF(II)25 temperature-sensitive mutant alleles individually affect the expression of between 18 and 33% of genes, whereas taken together they affect 64% of all class II genes. Thus, different yTAF(II)25 mutations induce distinct phenotypes and affect the regulation of different subsets of genes, demonstrating that no individual TAF(II) mutant allele reflects the full range of its normal functions.

Base Composition↗

PubMed2002

Distinct functions of TBP and TLF/TRF2 during spermatogenesis: requirement of TLF for heterochromatic chromocenter formation in haploid round spermatids.

TLF (TBP-like factor) is a protein commonly thought to belong to the general transcription initiation complex. TLF is evolutionarily conserved and has been shown to be essential for early development in C. elegans, zebrafish and Xenopus. In mammals however, TLF has a specialised function, as revealed by targeted mutation of the gene in the mouse germline. The TLF mutation elicits a complete arrest of late spermiogenesis and increased haploid cell apoptosis. We explored in more detail the molecular function that TLF plays in the differentiation program of male germ cells. A comparison of TBP and TLF reveals drastic differences, both in their temporal expression pattern and in their intracellular location. While TBP is ubiquitously expressed, TLF expression is strictly developmentally regulated, being very high in late pachytene spermatocytes, suggesting a function prior to the apoptosis of the haploid cells. A refined study of TLF-deficient mice reveals defective acrosome formation in early stage spermatids. Most importantly, our results uncover an unsuspected function of TLF in chromatin organisation. Indeed, early spermatids in TLF-deficient mice display a fragmentation of the chromocenter, a condensed structure formed by the association of centromeric heterochromatin and containing the HP1 proteins. This defect is likely to be the primary cause of spermatogenic failure in the TLF mutant mice.

Acrosome↗

PubMed2001

NF-Y recruitment of TFIID, multiple interactions with histone fold TAF(II)s.

The nuclear factor y (NF-Y) trimer and TFIID contain histone fold subunits, and their binding to the CCAAT and Initiator elements of the major histocompatibility complex class II Ea promoter is required for transcriptional activation. Using agarose-electrophoretic mobility shift assay we found that NF-Y increases the affinity of holo-TFIID for Ea in a CCAAT- and Inr-dependent manner. We began to dissect the interplay between NF-Y- and TBP-associated factors PO1II (TAF(II)s)-containing histone fold domains in protein-protein interactions and transfections. hTAF(II)20, hTAF(II)28, and hTAF(II)18-hTAF(II)28 bind to the NF-Y B-NF-YC histone fold dimer; hTAF(II)80 and hTAF(II)31-hTAF(II)80 interact with the trimer but not with the NF-YB-NF-YC dimer. The histone fold alpha2 helix of hTAF(II)80 is not required for NF-Y association, as determined by interactions with the naturally occurring splice variant hTAF(II)80 delta. Expression of hTAF(II)28 and hTAF(II)18 in mouse cells significantly and specifically reduced NF-Y activation in GAL4-based experiments, whereas hTAF(II)20 and hTAF(II)135 increased it. These results indicate that NF-Y (i) recruits purified holo-TFIID in vitro and (ii) can associate multiple TAF(II)s, potentially accommodating different core promoter architectures.

Animals↗