9423994 Raper The aim of this research is to understand how a simple eukaryote distinguishes itself from many nonselves in regulating mating and development. The specific objective is to discover the molecular mechanism by which the multiallelic B mating-type genes trigger sexual development in the mushroom-type fungus Schizophyllum commune. The B genes reside in two linked loci, B( and B(, each of which has nine different specificities in the world-wide population. A mating pair must be heteroallelic at either B( or B( to be compatible: any of 36 possible pairings of different specificities at either locus results in initiation of the identical developmental pathway. How is this possible? The recent cloning and sequencing of B(1 has revealed genes for putative pheromones and a pheromone receptor similar to those found in other fungi; all previously described fungal systems, however, possess only two allelic versions of such genes. It is likely that the basis for multispecificity of the B mating-type loci in S. commune is a unique system of multiple pheromone and pheromone receptor genes which act as master regulators of sexual morphogenesis. Evidence for other linked genes involved in specific events of sexual morphogenesis has been produced by a mutational dissection of the B(3 and B(2 loci. It is hypothesized that these other genes act downstream in a pheromone response pathway to affect particular steps in B-regulated development. The focus of this project is to test these hypotheses by characterizing the functional genetic components of the B(3 and B(2 loci. These will be compared with the B(1 and B(1 loci as part of a collaborative effort with two European laboratories. The number and kind of genetic elements that define given specificities of B( and B( is being determined by using standard techniques of DNA sequencing and DNA-mediated transformation of Schizophyllum. Preliminary analyses of the coding regions of relevant genes will be obtained by in vitro rnutagenesis and cDNA sequ encing. The existing deletion mutations within the loci will be used to isolate and characterize genes that affect specific developmental events in the B-regulated pathway. Genes of interest will be identified by using a set of overlapping clones within the wild-type B(3 - B(2 region as probes to determine differences in mutated versus progenitor DNA. Mutant strains will be used as transformation recipients to test for function of the wild-type genes. %%% Preliminary evidence suggests that B gene regulation of self/nonself recognition in S. commune is based on a ligand/receptor system similar to those known to regulate cell-to-cell communication and differentiation in a broad range of organisms. This study will take advantage of a unique opportunity to define the genetic determinants of what appear to be multiple versions of such molecules in a genetically accessible organism. *** ??
