An Investigation On The High Pka Activity And Heat Shock Resistance Of Saccharomyces Cerevisiae

There are two signal pathways in yeast cells associated with the cAMP, one is mediated by heterotrimeric G proteins and the other is mediated by small G proteins. In S. cerevisiae, Ras-cAMP signal pathway plays an important role in metabolism, proliferation, differentiation and stress resistance. The activity of PKA increases with the level of the activity of Ras protein. PKA is a serine/threonine kinase, and it can phosphorylate the serine residues and the threonine residues of the target protein. PKA modulates the cells'response to extracellular nutrient condition and stress through phosphorylation. Studyies have shown that the resistance to heat shock of S. cerevisiae depends on the intracellular PKA activity. In the case of high PKA activity, yeast cells'resistance to heat shock significantly lower than that of wild type. This work is based on the strain W303-1a YCp22RAS2Val19, insertingmTn-lacZ/LEU2 mutant library in any part of the chromosome of this strain to make transposons. When mTn library insterts into W303-1a YCp22RAS2Val19, chromosome, the insertion may happens at the ORF of heat shock resistance genes or the sequence of cis-acting elements. In this case, the ability of heat shock of the strains may change. The purified transformants are tested by heat shock experiments to check their heat shock resistance and we identify six mutants that have reversed heat shock resistant. ZL7, ZL9 and ZL13, these three mutants can tolerate heat shock up to 6min. ZL10, ZL11 and ZL16 have 3min heat shock tolerance. ZL7 mutant has no NOP7 and RAS2 activity; ZL9 mutant has no ULP2 activity; ZL10 and ZL16 have no NFS1 activity; ZL11 has no TPK1 activity and ZL13 has no TIM9 activity.