THE GTP-BINDING PROTEIN G-ALPHA(S) IS PRESENT IN DORMANT SPORES AND EXPRESSED DIFFERENTIALLY DURING SPORE GERMINATION OF THE FUNGUS PHYCOMYCES-BLAKESLEEANUS

A DNA sequence homologous to a G alpha(s) DNA probe, and the correspon ding G alpha(s) protein (stimulatory alpha-subunit of GTP-binding prot ein) were detected in Phycomyces blakesleeanus. The protein was demons trated in membrane fractions of dormant spores of this fungus using th ree different experimental approaches. Photoaffinity-labelling experim ents with [alpha-P-32]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 specifi c antibody against mammalian G alpha(s). These results indicate that G alpha(s) (56 kDa) is present in dormant spores of P. blakesleeanus. U sing the ADP-ribosylation and Western blotting assays, G alpha(s) was detected during all stages of spore germination before the hyphae beca me highly branched, but it was not detected in the branched hyphae tha t formed 18 h after the initiation of spore germination. Therefore, G alpha(s) is expressed differentially during Phycomyces development.