Involvement of Snf7 and Rim101 in regulation of TIR1 and anaerobically up-regulated genes in yeast

Despite the scientific and applied interest in anaerobic metabolism of Saccharomyces cerevisiae, not all genes whose transcription is up-regulated under anaerobic conditions have yet been linked to known transcription factors. Experiments with a reporter construct in which the promoter of the anaerobically up-regulated TIR1 gene was fused to LacZ revealed a complete loss of anaerobic up-regulation in a snf7 mutant. Anaerobic up-regulation was restored by expression of a truncated allele of RIM101 that encodes for a constitutively active Rim101p transcription factor. Analysis of LacZ expression in several deletion mutants confirmed that the effect of Snf7p on anaerobic up-regulation of TIR1 involved Rim101p and did not require a functional multi-vesicular body sorting pathway (in which Snf7p also participates). Transcriptome analysis in anaerobic chemostat cultures revealed that 26 additional genes exhibited a Snf7p/Rim101p dependent anaerobic up-regulation. Since, in its activated form, Rim101p is generally known as a transcriptional repressor, its role in anaerobic up regulation of TIR1 and other anaerobic yeast genes must involve additional factors. Further studies with deletion mutants in NRG1, NRG2 and SMP1, which were previously shown to be regulated by Rim101p, showed that these genes were not involved in the regulation of TIR1. However, the aerobic repression mechanism of TIR1 involved the general repressor Ssn6p-Tup1p complex. The physiological relevance of Snf7p/Rim101p-mediated transcriptional up-regulation of several genes in anaerobic yeast cultures was evident from reduced growth of a snf7 under anaerobic conditions.

23

Snoek IS, Tai SL, Pronk JT, Yde Steensma H, Daran JM