Abstract

Incorporation into the wall of Candida albicans Ssrl, a GPI-dependent protein, was investigated by construction of different truncated genes for which the three potential omega sites (S-199, S-215 and G(216)) and the corresponding omega + 1 and omega + 2 were eliminated or modified. Cells of the C. albicans ssrl Delta mutant were transformed with pADH-pl harboring the truncated versions of CaSSR1, pADHA-Delta CaSSR1t((217-234)) (lacking a C-terminal hydrophobic stretch of 18 aa including the putative omega + 2 and w + 1. w + 2 of S')15 and G216) or pADH-ACaSSR1t((199-201)) (lacking three serine residues), and their walls were analyzed for the protein. Results suggested that the three serine residues are essential for incorporation of CaSsr1 into the wall P-glucan. This interpretation was confirmed when the truncated protein CaSsr1pt((199-201)) was found in the spent medium. The transcription profile of the 6039 genes in C. albicans ssrl Delta showed that seven genes are upregulated (>= 1.4-fold), including SRP54 (a signal recognition particle subunit), IPF29 (a zinc finger protein) and PTR3 (a transcriptional regulator), whereas 27 genes are downregulated (<= 0.7-fold), including IPF6318 (a beta-glucosidase) and SOUI (a sorbitol utilization protein). Additional genes showed a reduced increase, or decreased expression, suggesting that some current orphan genes may have unknown cell wall functions. In addition, a compensatory mechanism would appear to occur, as a substantial increase in the amount of beta-1,3-glucan (2.34-fold) was detected in the cell wall of the mutant cells. (c) 2005 Elsevier SAS. All rights reserved.