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Abstract
A DNA sequence homologous to a Gas DNA probe, and the corresponding Gas protein (stimulatory a-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 [a-32P]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 Gas. These results indicate that Gas (56 kDa) is present in dormant spores of P. blakesleeanus. Using the ADP-ribosylation and Western blotting assays, Gas 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, Gas is expressed differentially during Phycomyces development.
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