Regulation of hsp90 and hsp70 genes during antheridiol-induced hyphal branching in the oomycete Achlya ambisexualis.

When mycelia of Achlya ambisexualis J. Raper strain E87 were undergoing antheridial branching, a marked increase was observed in the levels of transcript populations encoding the heat shock protein chaperone Hsp90 and transcript populations encoding three different Hsp70-family heat shock protein chaperones, respectively. Although up to 90% of hyphae in the hormone-treated thalli were undergoing antheridial branching, no similar increase in the level of transcripts encoding actin was observed. Nuclear run-on assays demonstrated that the observed antheridiol-induced increases in the levels of the chaperone RNAs resulted from increased transcription. Although not tested for function, the nucleotide sequence of the 5' flanking region of each of the two A. ambisexualis hsp90 genes revealed a diversity of sequences and motifs similar or identical to the sequences of known transcription factor response elements. Among these potential response element sequences observed in the A. ambisexualis genes were motifs observed also in animal steroid hormone response elements. Surrounding the primer-extension determined transcription start site of each A. ambisexualis hsp90 gene was a 16-nucleotide sequence that matched in 14 out of 16 nucleotides a sequence found in the transcription initiation region of many different oomycete genes.