Mutated A and B incompatibility factors of Coprinus cinereus (Amut and Bmut) were recovered from fruit bodies produced on common-A and common-B heterokaryons, respectively, following mutagenesis. The Amut hyphal cells were either uninucleate or binucleate and had pseudoclamps irregularly scattered along the hyphae. The Bmut hyphal cells were predominantly uninucleate and had no clamp structures. Amut Bmut double mutants constructed from these Amut and Bmut strains were predominantly binucleate, had true clamps, and gave rise to fertile fruit bodies indistinguishable from those of wild-type dikaryons. Although these Amut Bmut strains resembled in most respects a normal dikaryon, they produced abundant oidiophores and oidia like the monokaryons. The oidia were uninucleate, and possessed the potential to grow into fertile homokaryons with the above characteristics.

Adenylate cyclase and phosphodiesterase activities were assayed during the course of sexual reproduction in Coprinus cinereus. High levels of adenylate cyclase activity and low levels of phosphodiesterase activity were found in all dikaryons, in Amut Bmut strains, and in the monokaryotic fruiter Fist. Corresponding to this, a high level of cAMP was found in these strains. On the other hand, low levels of cAMP were found in semi-compatible heterokaryons (common-A and common-B), and in Amut and Bmut strains, where the events leading to sexual morphogenesis had been switched on only partially. CAMP-binding and CAMP-dependent protein kinase activities were detected in the dikaryons, and in Amut Bmut and Fist strains, but were negligible in the sexually sterile strains. The results indicated that both A and B factors are involved in the coordinate regulation of adenylate cyclase, phosphodiesterase, and CAMPdependent protein kinase during fruit body formation. ~ ~ Abbreviation : 8-N,-[3H]cAMP, 8-azidoadenosine 3',5'-[3H]monophosphate. 0001-2723 0 1985 SGM

The phosphorylation of a cellular protein of 46,000 daltons was stimulated by the addition of adenosine 3',5'-cyclic monophosphate (cAMP) in the sexually fertile dikaryotic and Amut Bmut strains of Coprinus cinereus, but not in the sexually sterile Amut, Bmut, and wild-type monokaryons. Cyclic AMP-dependent inhibition of glutamate dehydrogenase was observed only in the dikaryotic and Amut Bmut strains, but not in the Amut, Bmut, and monokaryotic strains.Extremely low levels of ATP and cAMP were sufficient to bring about half maximal inactivation of glutamate dehydrogenase.The results indicate that glutamate dehydrogenase is an endogenous substrate for cAMP-dependent protein kinase which is regulated by the incompatibility factors.In eukaryotic organisms including several fungi, adenosine 3',5'-cyclic monophosphate (cAMP) was found to exert its effects through the activation of cAMPdependent protein kinase which then governed the action of several proteins including key metabolic enzymes through phosphorylation (1-5). In Coprinus cinereus as in other eukaryotes, the regulatory subunit of cAMP-dependent protein kinase was found to be the receptor of cAMP (6). Also in relation to previous observations that a high level of cAMP correlated with fruiting ability (7-10), a high level of cAMP-dependent protein kinase activity was reported to be correlated with fruiting ability (6).Sexual morphogenesis in the tetrapolar basidiomycetes is known to be triggered by the switching `on' of both A-and B-factor controlled events. In C. cineretts, mutants of A and B incompatibility factors (Amut and Bmut) have been isolated (11-13). These Amut and Bmut mutations led to constitutive expression of events regulated by the respective incompatibility factor and resulted in the conversion of self-incompatible strains to self-compatible ones (13). It was thus hoped 339