MUTATION THI81 CAUSING A DEFICIENCY IN THE SIGNAL-TRANSDUCTION OF THIAMINE PYROPHOSPHATE IN SACCHAROMYCES-CEREVISIAE

We isolated a strain carrying a recessive constitutive mutation (thi81 ) for the expression of thiamine metabolism in Saccharomyces cerevisia e. The thi81 mutant exhibits significant thiamine transport, thiamine- repressible acid phosphatase (T-rAPase) activities and significant act ivities of enzymes involved in thiamine biosynthesis which are repress ed in the wild-type strain in medium supplemented with thiamine (2x10( -7) M). The thi81 mutant exhibited the same level of thiamine pyrophos phokinase activity and intracellular thiamine pyrophosphate concentrat ion as the wild-type strain in medium supplemented with exogenous thia mine. The mutant strain constitutively produced PHO3 mRNA encoding T-r APase in medium supplemented with thiamine. These results suggest that the thi81 mutant lacks a negative factor involved in the regulation o f the genes encoding proteins involved in yeast thiamine metabolism.