title: Ras signaling is required for serum-induced hyphal differentiation in Candida albicans.
abstract: Serum induces Candida albicans to make a rapid morphological change from the yeast cell form to hyphae. Contrary to the previous reports, we found that serum albumin does not play a critical role in this morphological change. Instead, a filtrate (molecular mass, <1 kDa) devoid of serum albumin induces hyphae. To study genes controlling this response, we have isolated the RAS1 gene from C. albicans by complementation. The Candida Ras1 protein, like Ras1 and Ras2 of Saccharomyces cerevisiae, has a long C-terminal extension. Although RAS1 appears to be the only RAS gene present in the C. albicans genome, strains homozygous for a deletion of RAS1 (ras1-2/ras1-3) are viable. The Candida ras1-2/ras1-3 mutant fails to form germ tubes and hyphae in response to serum or to a serum filtrate but does form pseudohyphae. Moreover, strains expressing the dominant active RAS1(V13) allele manifest enhanced hyphal growth, whereas those expressing a dominant negative RAS1(A16) allele show reduced hyphal growth. These data show that low-molecular-weight molecules in serum induce hyphal differentiation in C. albicans through a Ras-mediated signal transduction pathway.
authors.affiliation: Whitehead Institute for Biomedical Research/Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Feng
authors.forename: E
authors.initials: E
authors.lastname: Summers
authors.forename: B
authors.initials: B
authors.lastname: Guo
authors.forename: G
authors.initials: G
authors.lastname: Fink
mesh_terms: D000595:Amino Acid Sequence; D001769:Blood; D002176:Candida albicans / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003470:Culture Media; D005656:Fungal Proteins; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000187:drug effects; D016296:Mutagenesis; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D012709:Serum Albumin / Q000494:pharmacology; D015398:Signal Transduction; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D003470:Culture Media; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D012709:Serum Albumin; C489014:RAS1 protein, S cerevisiae; C489015:RAS2 protein, S cerevisiae; D018631:ras Proteins