NMT2 OF FISSION YEAST - A 2ND THIAMINE-REPRESSIBLE GENE CO-ORDINATELYREGULATED WITH NMT1

We previously described a screen for thiamine-repressible genes in Sch izosaccharomyces pombe and reported on one such gene, nmt1, required f or thiamine biosynthesis. Here we describe a second gene, nmt2, recove red in the same screen. Disruption of nmt2 also resulted in thiamine a uxotrophy, indicating a role for the nmt2 gene product in thiamine bio synthesis. Both genes are highly transcribed in minimal medium and rep ressed in medium containing thiamine, and nuclear 'run-on' experiments confirm that expression in both cases is controlled by the rate of tr anscription initiation. The virtually identical kinetics of induction and repression suggest that the two genes are co-ordinately regulated. Sequence comparison of the two promoters reveals a canonical TATA box , downstream of which is a perfectly conserved 11 bp element. Transcri pt mapping experiments show that transcription initiation of both gene s is centred on this element.