REGULATION OF TRANSCRIPTION OF THE GENE CODING FOR PEROXISOMAL 3-OXOACYL-COA THIOLASE OF SACCHAROMYCES-CEREVISIAE

Transferring Saccharomyces cerevisiae cells from glucose- to oleate-containing growth media results in a significant increase in the number and volume of peroxisomes. To investigate this proliferation process we studied the transcriptional regulation of the gene coding for peroxisomal 3-oxoacyl-CoA thiolase (EC 2.3.1.16) in response to the switch in carbon source. Expression was proved to be repressed during growth on glucose, derepressed during growth on glycerol, and induced during growth on oleate as the sole carbon source. By deletion and mutational analysis of sequences upstream of this gene, we have identified a region which is involved in the regulation of transcription. It is contained within a 52-base-pair sequence, UAS(T52) (upstream activation sequence thiolase 52), located between 203 and 151 nucleotides upstream of the translational initiation codon. This seuqence proved to be required for repression, derepression and induction of transcription, and was able to activate transcription from the truncated version of the heterologous iso-1-cytochrome-c (CYC1) promoter in a similar way as in the wild-type promoter context. Sequence comparison revealed that the UAS(T52) contained a sequence motif ('beta-oxidation box') that is very similar to sequences located in the 5'-upstream regions of the genes coding for two other beta-oxidation enzymes of S. cerevisiae: the peroxisomal acyl-CoA oxidase and the peroxisomal trifunctional beta-oxidation enzyme of S. cerevisiae. Mutational analysis of the 'beta-oxidation box' indicates that this sequence motif acts as a UAS in vivo. Sequence comparison also revealed that just upstream of the 'beta-oxidation box', between positions - 213 and -201, a potential binding site occurred for the yeast multifunctional autonomously replicating sequence binding factor ABF1. Gel-retardation-competition experiments indicate that ABF1 binds specifically to this sequence.