Regulation of the Saccharomyces cerevisiae INO1 gene: Novel insights into a hallmark of eukaryotic transcription regulation

Transcription regulation in eukaryotes is a complex process governed by the concerted action of different factors. The work in this thesis is focused on transcriptional regulation in Saccharomyces cerevisiae. I analyzed the regulation of the phospholipid biosynthetic gene INO1 , which has been a model gene for transcription studies for over three decades. Some major questions that I have addressed are: what kinds of cis regulatory sequences and trans factors are important for regulation of INO1? What is the sequence of events in this regulation? How is the recruitment of these trans factors consequential for INO1 transcription? I present my results here for the role of the basic helix loop helix transcription factor (bHLH) family in coordinated regulation of INO1 transcription. I report that the centromeric binding factor 1 (Cbf1p) together with two other members of the bHLH protein family, Ino2p and Ino4p, are required for efficient derepression of INO1 transcription. Together these bHLH transcription factors recruit the ISW2 chromatin-remodeling complex onto the INO1 promoter to drive productive transcription from the INO1 locus. My efforts in studying the regulation of INO1 led me to study the regulation of SNA3, a gene found in tandem upstream (→→) to the INO1 gene and regulated by the same environmental conditions as INO1. Studies on the mechanism of coregulation of adjacent genes in budding yeast have been largely speculative. I provide evidence that the same bHLH proteins which regulate INO1 also regulate SNA3, albeit differentially. Significantly, my results also show that the regulation of both SNA3 and INO1 is dictated from the intergenic region between the two genes. This is a novel mechanism of transcription regulation in yeast as regulation from downstream of ORF is unknown in yeast. Thus, my results with both SNA3 and INO1 provide novel details on how the process of transcription is regulated in response to an environmental cue