Expression of TPK1 and TPK2 genes encoding PKA catalitic subunits during growth and morfogenesis in Candida albicans

SOUTO, G.; GIACOMETTI, R.; SILBERSTEIN, S.; GIASSON, L.; CANTORE, M.L; PASSERON, S.

YEAST

Año: 2006 p. 591 - 603

0749-503X

The transcript levels of Candida albicans TPK1 and TPK2 genes, encoding PKA catalytic subunits, as well as phosphotransferase activity were measured during vegetative growth and yeast-to-mycelial transition in N-acetylglucosamine (GlcNAc) liquid inducing medium at 37°C in the parental strain CAI4 and in two derived homozygous mutant strains having TPK1 or TPK2 deleted. Levels of TPK1 and TPK2 mRNAs were shown to increase steadily during exponential growth of the yeast form remaining high in the stationary phase. We found that a sharp increase in TPK1 mRNA levels correlated with the onset of germ-tube formation in CAI4 and tpk2@/tpk2@ strains, while no significant transcript variations were observed in control cultures not undergoing cell filamentation. Our study indicates that in the mutant strain tpk2@/tpk2@ changes in PKA activity roughly correlated with TPK1 mRNA expression levels. We also show that tpk1@/tpk1@mutant strain exhibited a delayed morphogenetic shift in comparison with CAI4 and tpk2@/tpk2@strains, reinforcing the idea that Tpk1p is important for the onset of filamentous growth. Interestingly, it was found that the TPK2 gene was transcribed predominantly as a 1.8 kb mRNA but also as a less abundant 1.4 kb mRNA during vegetative growth and during germ-tube formation. Analysis of the sequence of the TPK2 3 ́ untranslated region revealed the presence of three putative consensus polyadenylation signals. 3’-RACE analysis of the 3 ́ untranslated region of the TPK2 mRNA yielded three bands of approximately 0.75, 0.55 and 0.45 kbp. The fact that the three poly(A) sites are used in vivo, strongly suggests that they might be part of a transcriptional control mechanism.