Functional Characterization of the MKC1 Gene of Candida albicans, Which Encodes a Mitogen-Activated Protein Kinase Homolog Related to Cell Integrity

Abstract

Mitogen-activated protein (MAP) kinases represent a group of serine/threonine protein kinases playing a central role in signal transduction processes in eukaryotic cells. Using a strategy based on the complementation of the thermosensitive autolytic phenotype of slt2 null mutants, we have isolated a Candida albicans homolog of Saccharomyces cerevisiae MAP kinase gene SLT2 (MPK1), which is involved in the recently outlined PKC1-controlled signalling pathway. The isolated gene, named MKC1 (MAP kinase from C. albicans), coded for a putative protein, Mkc1p, of 58,320 Da that displayed all the characteristic domains of MAP kinases and was 55% identical to S. cerevisiae Slt2p (Mpk1p). The MKC1 gene was deleted in a diploid Candida strain, and heterozygous and homozygous strains, in both Ura¹ and Ura² backgrounds, were obtained to facilitate the analysis of the function of the gene. Deletion of the two alleles of the MKC1 gene gave rise to viable cells that grew at 28 and 37&C but, nevertheless, displayed a variety of phenotypic traits under more stringent conditions. These included a low growth yield and a loss of viability in cultures grown at 42&C, a high sensitivity to thermal shocks at 55&C, an enhanced susceptibility to caffeine that was osmotically remediable, and the formation of a weak cell wall with a very low resistance to complex lytic enzyme preparations. The analysis of the functions downstream of the MKC1 gene should contribute to understanding of the connection of growth and morphogenesis in pathogenic fungi.