Presence of DNA sequence homologous to RAS gene in the aquatic fungus Achlya ambisexualis: Possible role in sporangiogenesis

The water mold Achlya ambisexualis reproduces asexually by the formation of zoospores produced in sporangia. The differentiation of vegetative hyphae to sporangia involves a series of morphologic and biochemical changes. Thus far, very little is known about the regulation of sporogenesis in this organism. Using DNA-DNA and DNA-RNA hybridizations, we investigated the presence of DNA sequences homologous to the yeast RAS gene in A. ambisexualis. A 1.8-kilobase (kb)HindIII fragment containing the complete RAS^sc1 gene specifically hybridized to BamHI, PstI, and SalI digested A. ambisexualis DNA. RNA blot analysis revealed the presence of a detectable level of RNA transcript (1.3 kb) that hybridizes to RAS^sc1, only in differentiating mycelia. In addition, the³⁵S-labeled polypeptide profile of sporulating hyphae differs from that of vegetative hyphae. The selective transcription of 1.3-kb RNA during sporangiogenesis indicates that it may play some significant role in the asexual sporulation in A. ambisexualis.