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T J Hofmann

Publications and source records attributed to T J Hofmann.

9 recordsLinked to original sources
PubMed1996

The TAL1/Scl basic helix-loop-helix protein blocks myogenic differentiation and E-box dependent transactivation.

The TAL1 gene is transcriptionally activated by chromosomal translocation in the most common genetic lesion associated with T-cell acute lymphoblastic leukemia. TAL1 encodes a bHLH protein that exhibits sequence-specific DNA binding activity when it forms dimers with another bHLH protein such as E2A. We show that ectopic expression of TAL1 blocks the ability of the bHLH gene myogenin to induce myotube differentiation in C3H10T1/2 cells. Cotransfection of TAL1 with either myogenin or E2-5 suppresses the transcriptional activation function of each gene on its respective reporter constructs. TAL1 was as effective as Id in both transcriptional suppression and inhibition of differentiation. Deletion of the C-terminal domain of TAL1 reduces or eliminates its ability to suppress transcription while preserving the bHLH domain that determines the sequence-specificity of DNA binding. These data suggest that the C-terminal domain of TAL1 may directly mask the transactivation domain of E2A-related proteins. Since E2A-related genes are involved in lymphocyte differentiation, the dominant inhibition of E2A-related proteins may be the primary mechanism by which the TAL1 oncogene promotes leukemia.

Animals↗
PubMed1995

An essential domain of the c-myc protein interacts with a nuclear factor that is also required for E1A-mediated transformation.

Cell transformation by nuclear oncogenes such as c-myc presumably involves the transcriptional activation of a set of target genes that participate in the control of cell division. The function of a small evolutionarily conserved domain of the c-myc gene encompassing amino acids 129 to 145 was analyzed to explore the relationship between cell transformation and transcriptional activation. Deletion of this domain inactivated the c-myc oncogene for cell transformation while retaining the ability to activate transcription of either myc consensus binding sites or a GAL4-dependent promoter when the c-myc N-terminus was fused to the GAL4 DNA-binding domain. Point mutations that altered a conserved tryptophan (amino acid 136) within this domain had similar effects. Expression of the wt c-Myc N terminus (amino acids 1 to 262) as a GAL4 fusion was a dominant inhibitor of cell transformation by the c-myc oncogene, and this same domain also inhibited transformation by the adenovirus E1A gene. Surprisingly, deletion of amino acids 129 to 145 eliminated the dominant negative activity of GAL4-Myc on both c-myc and E1A transformation. Expression of the GAL4-Myc protein in Cos cells led to the formation of a specific complex between the Myc N terminus and a nuclear factor, and this complex was absent with the dl129-145 mutant. These results suggest that an essential domain of the c-Myc protein interacts with a specific nuclear factor that is also required for E1A transformation.

Adenovirus E1A Proteins↗
PubMed1993

Formation of the 3' end of yeast mitochondrial mRNAs occurs by site-specific cleavage two bases downstream of a conserved dodecamer sequence.

Mitochondrial mRNAs in yeast arise by processing of polygenic primary transcripts at a conserved dodecamer sequence (5'-AAUAAPyAUUCUU-3'). Previous results indicated that processing at dodecamer sites interrupted the sequence implying that it functioned primarily as a signal for 3' end formation of mRNAs. We have determined the precise cleavage site for RNAs processed at the dodecamer sequences associated with the oli1 gene and the omega intron of the 21S rRNA gene. In both cases cleavage occurred two bases downstream of the site. Hydrolysis left the PO4 group attached to the 3' terminus of the cleavage products. These results demonstrate for the first time that mature mitochondrial mRNAs terminate with an intact dodecamer sequence. In light of the recent identification of a protein complex within mitochondria that binds to RNAs terminating with an intact dodecamer sequence, these results support the idea that the dodecamer sequence functions not only within pre-mRNAs as a processing site, but within mature mRNAs as well, possibly for the stabilization and/or translation.

Base Sequence↗
PubMed1988

Purification and properties of the major nuclease from mitochondria of Saccharomyces cerevisiae.

The vast majority of nuclease activity in yeast mitochondria is due to a single polypeptide with an apparent molecular weight of 38,000. The enzyme is located in the mitochondrial inner membrane and requires non-ionic detergents for solubilization and activity. A combination of heparin-agarose and Cibacron blue-agarose chromatography was employed to purify the nuclease to approximately 90% homogeneity. The purified enzyme shows multiple activities: 1) RNase activity on single-stranded, but not double-stranded RNA, 2) endonuclease activity on single- and double-stranded DNA, and 3) a 5'-exonuclease activity on double-stranded DNA. Digestion products with DNA contain 5'-phosphorylated termini. Antibody raised against an analogous enzyme purified from Neurospora crassa (Chow, T. Y. K., and Fraser, M. (1983) J. Biol. Chem. 258, 12010-12018) inhibits and immunoprecipitates the yeast enzyme. This antibody inhibits 90-95% of all nuclease activity present in solubilized mitochondria, indicating that the purified nuclease accounts for the bulk of mitochondrial nucleolytic activity. Analysis of a mutant strain in which the gene for the nuclease has been disrupted supports this conclusion and shows that all detectable DNase activity and most nonspecific RNase activity in the mitochondria is due to this single enzyme.

Cations, Divalent↗
PubMed1988

Construction of a yeast mutant lacking the mitochondrial nuclease.

The nuclear gene from Saccharomyces cerevisiae that encodes the major mitochondrial nuclease was cloned. Gene sequences were identified from a lambda gt11 library by antibodies specific to the mitochondrial nuclease. DNA from the phage recombinant was used to isolate the entire nuclease gene from a plasmid library. Yeast strains containing the nuclease gene on a multicopy plasmid vector overproduced mitochondrial nuclease 20-40 times relative to a wild-type strain. Strains containing a null allele of the nuclease gene lacked all traces of mitochondrial nuclease. Both cell types, however, were phenotypically wild-type indicating that the nuclease is not an essential enzyme for mitochondrial function. The locus encoding the mitochondrial nuclease is termed NUC1.

Endonucleases↗
PubMed1988

Sequence and expression of NUC1, the gene encoding the mitochondrial nuclease in Saccharomyces cerevisiae.

The DNA sequence and studies on the expression of the NUC1 gene from Saccharomyces cerevisiae are presented. The NUC1 locus is located in the distal portion of the left arm of Chromosome X and encodes the major nuclease found in mitochondria. The inferred amino acid sequence of NUC1 predicts that the nuclease is basic, rich in prolines, of average hydrophobicity, and has a molecular weight for the primary translation product of 37,209 daltons. NUC1 is very poorly expressed, consistent with the codon usage bias determined from the DNA sequence and our previous determination of the number of enzyme molecules per cell. Mapping of the 5' terminus of the NUC1 mRNA reveals that the mRNA has a long 400 base untranslated leader in which are found three open reading frames, each initiated by an AUG. The possibility that these upstream open reading frames contribute to the poor expression of the NUC1 gene is discussed.

Amino Acid Sequence↗