ROLE OF THE MYB-LIKE PROTEIN BAS1P IN SACCHAROMYCES-CEREVISIAE - A PROTEOME ANALYSIS

The effect of extracellular adenine and the role of the transcriptiona l activator Bas1p on expression of the yeast genome was assessed by tw o-dimensional (2D) analysis of the yeast proteome. These data combined with LacZ fusions and northern blot analysis allow us to show that sy nthesis of enzymes for all 10 steps involved in purine de novo synthes is is repressed in the presence of adenine and requires BAS1 and BAS2 for optimal expression. We also show that expression of ADE12 and ADE1 3, the two genes required for synthesis of AMP from inosine 5'monophos phate (IMP), is co-regulated with the de novo pathway genes. The same combined approach, used to study histidine biosynthesis gene expressio n, showed that HIS1 and HIS4 expression is co-regulated with purine bi osynthesis genes whereas HIS2, HIS3, HIS5 and HIS6 expression is not. This work, together with previously published data, gives the first co mprehensive overview of the regulation of purine and histidine pathway s in a eukaryotic organism. Finally, the expression of two pyrimidine biosynthesis genes URA1 and URA3 was found to be severely affected by bas1 and bas2 mutations in the absence of adenine, establishing a regu latory link between the two nucleotide biosynthesis pathways.