Induction of hsp70 in the fungus Rhizopus nigricans

We characterised two positive clones, RnH20/2 and RnH2/3, isolated from the cDNA library prepared from the fungus Rhizopus nigricans previously exposed to heat shock. Nucleotide sequences of both cDNA clones contained open reading frames for polypeptides with a significant amino acid identity to each other and to cytoplasmic members of Hsp70s from different eukaryotic organisms. Northern blot analysis, using a fragment of RnH2/3 as a probe, revealed that in the fungus R. nigricans the Hsp70 transcripts were inducible with deoxycorticosterone and testosterone as well as with heat stress, ethanol, CuSO(4), and H(2)O(2). This is the first report on isolation of cDNAs encoding Hsp70s from the fungal phylum Zygomycota.