Molecular organisation of an A mating type factor of the basidiomycete fungus Coprinus cinereus

The A alpha 3 and A beta 3 genes, which together constitute the A42 mating type factor of Coprinus cinereus , were isolated from a cosmid genomic library by walking 50 kb, a map distance of 0.5 units, from the closely linked metabolic gene pab-1. Cosmid clones having A gene function were identified by transformation into compatible A6 ( alpha 2 beta 2) and A5 ( alpha 1 beta 1) host cells where either alpha 3 and beta 3 was expected to elicit the A factor-regulated development of unfused clamp cells. DNAs were digested with various enzymes before transformation in order to identify the smallest fragments containing an active alpha 3 or beta 3 gene. Two non-overlapping fragments were identified as containing the alpha 3 and beta 3 genes respectively. Southern hybridisation analyses showed that these two cloned genes had no detectable sequence homology, and that there was little or no hybridisation to the alpha and beta gene alleles that constitute the A5 and A6 factors.