To understand the principles of control and selectivity in gene expression, the biochemical mechanisms by which promoter- and enhancer-binding factors regulate transcription by RNA polymerase II were analyzed. A general observed repressor of transcription was purified and identified as histone H1. Since many aspects of H1 binding to naked DNA resemble its interaction with chromatin, purified H1 bound to naked DNA was used as a model for the repressed state of the DNA template. Three sequence-specific transcription factors, Sp1, GAL4-VP16, and GAGA factor, were shown to counteract H1-mediated repression (antirepression). In addition, Sp1 and GAL4-VP16, but not the GAGA factor, activated transcription in the absence of H1. Therefore, true activation and antirepression appear to be distinct activities of sequence-specific factors. Furthermore, transcription antirepression by GAL4-VP16 was sustained for several rounds of transcription. These findings, together with previous studies on H1, suggest that H1 participates in repression of the genome in the ground state and that sequence-specific transcription factors induce selected genes by a combination of true activation and release of basal repression that is mediated at least in part by H1.

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Our previous studies have shown that Mucor racemosus possesses three genes (TEF-1, -2 and -3) for EF-1 alpha, and that all three genes are transcribed. However, the level of transcription varies markedly between the three genes, with TEF-1 mRNA levels being approximately two fold higher than TEF-3 and 6 fold higher than TEF-2. We have now completed the DNA sequence of both strands of all three genes and have found that these genes are highly homologous. TEF-2 and TEF-3 are more similar to each other than they are to TEF-1. The TEF-2 and the TEF-3 coding regions differ from TEF-1 at 30 and 37 positions respectively out of 1374 nucleotides. Twenty-six of these nucleotide substitutions were common to both TEF-2 and TEF-3, and the majority of the substitutions were clustered in the 5' region of the coding sequences. While the majority of these changes were silent, TEF-2 and TEF-3 differed from TEF-1 by having a lysine instead of a glutamate at amino acid position 41. In addition, TEF-2 and -3, but not TEF-1, each have an intron located near the 5' end of the coding region, although its size and sequence is not conserved between the two genes. All three genes have a conserved intron near the 3' end of the coding region. The sequence data have been analyzed with respect to the structure and function of EF-1 alpha in protein biosynthesis.

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