Nucleic Acids Research An ARS/silencer binding factor also activates two ribosomal protein genes in yeast

ABSTRACT GFI is an abundant yeast DNA-binding protein, capable of binding to both ARS sequences and to the upstream regions of a number of nuclear genes coding for mitochondria] proteins (Dorsman et al., Nucl. Acids Res., 16 [1988] 7287-7301). GFI binding sites conform to the consensus RTCRYN5ACG, an element also present in the binding sites of factors designated SUF and TAF. These factors act as trans-activators of the constitutive transcription of the genes for ribosomal proteins S33 and L3 respectively. We now present evidence that GFI, TAF and SUF are probably the same protein. We speculate that one of the functions of GFI is the adjustment of the expression of a number of gene families to cell growth rate. INTRODUCTION Transcription in eukaryotic cells is activated by a number of proteins acting in concert with RNA polymerase (see ref. 1 for review). In the yeast Saccharomyces cerevisiae a number of such transcriptional activators have been characterized both genetically and biochemically. Some of these, such as the GCN4 and GAL4 proteins (2,3), are specifically required for the expression of only a limited number of genes, while others, such as the PHO2 and TUF (alias RAP or GRF1) proteins (4-6) may act as global regulators of genes involved in many apparently unlinked metabolic activities. We have previously described the properties of two abundant DNA-binding proteins, desigated as GFI and GFTI (7). Both factors bind to the upstream regions of a number of nuclear genes coding for mitochondrial proteins, while GFI is in addition capable of binding to ARS sequences. Features of its recognition site suggest that GFI is identical to, or at least highly similar to two other DNA-binding proteins, namely SBF-B and ABFI, which were initially characterized in terms of their ability to bind to silencer and ARS elements respectively (8,9). More recently, we have noted that the consensus derived for the GFI binding site can also accommodate the recognition sequences for SUF and TAF, two other independently identified DNA-binding proteins that act as trans-activators of the constitutive transcription of the genes for ribosomal proteins S33 and L3 respectively (6,10). We now show by a combination of retardation-competition and binding site studies that GFI, TAF and SUF are likely to be the same protein. We suggest that GFI is a DNA binding protein with several different functions in cell division and transcriptional regulation. One of these may be the adjustment of the expression of a number of gene families with respect to cellular growth rate