A DNA sequence homologous to a Gα DNA probe, and the corresponding Gα protein (stimulatory -subunit of GTP-binding protein) were detected in Phycomyces blakesleeanus. The protein was demonstrated in membrane fractions of dormant spores of this fungus using three different experimental approaches. Photoaffinity-labelling experiments with [αP]GTP of the membrane fraction revealed two bands, of 56 and 32 kDa. The 56 kDa GTP-binding protein was detected by this method in all the stages of early development and growth investigated. Also, a spore protein of 56 kDa was ADP-ribosylated by cholera toxin, and a 56 kDa protein was detected by Western blotting with a specific antibody against mammalian Gα. These results indicate that Gα (56 kDa) is present in dormant spores of P. blakesleeanus. Using the ADP-ribosylation and Western blotting assays, Gα was detected during all stages of spore germination before the hyphae became highly branched, but it was not detected in the branched hyphae that formed 18 h after the initiation of spore germination. Therefore, Gα is expressed differentially during development.


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