Expression of TPK1 and TPK2 genes encoding PKA catalytic subunits during growth and morphogenesis in Candida albicans

The transcript levels of Candida albicans TPK1 and TPK2 genes, encoding PKA catalytic subunits, as well as phosphotransferase activity, were measured in the parental strain CAI4 and in homozygous tpk1 Delta and tpk2 Delta mutants during vegetative growth and during yeast-to-mycelial transition in N-acetylglucosamine liquid inducing medium at 37 degrees C. We observed two TPK2 transcripts, a major one of 1.8 kb and a minor one of 1.4 kb, and established by 3'-RACE that they originate from the recognition of the three polyadenylation signals present in the 3' untranslated region of the gene. During vegetative growth of CAN strain, the expression profiles of TPKI and TPK2 varied similarly, reaching maximal expression at the late logarithmic phase. TPKI mRNA levels were lower than those of TPK2 at all stages measured. In the corresponding homozygous tpk mutants, mRNA levels and the expression patterns of TPK1 and TPK2 were similar to those of CAN, suggesting that the loss of one catalytic isoform is not compensated by overexpression of the other. Changes in PKA specific activity roughly correlated with fluctuations of mRNA expression levels. During yeast-to-mycelial transition, a sharp increase in TPKI mRNA levels and in PKA-specific activity correlated with the onset of germ-tube formation in strain tpk2 Delta. We also showed that tpk1 Delta strain exhibited a delayed morphogenetic shift in comparison with CAI4 and tpk2 Delta strains in several liquid inducing media, reinforcing the idea that Tpk1p is important for faster germ-tube appearance. Copyright (c) 2006 John Wiley & Sons, Ltd.