A number of genes have been shown to be transcribed specifically during sporulation in Saccharomyces cerevisiae, yet their developmentalifnction is unknown. The SPRP gene is transcribed during only the late stages of sporulation. We have sequenced the SPRi gene and found that it has extensive DNA and protein sequence homology to the S. cerevisiae EXG1 gene which encodes an exo-1,3-0-glucanase expressed during vegetative growth (C. R. Vasquez de Aldana, J. Correa, P. San Segundo, A. Bueno, A. R. Nebrada, E.Mendez, and F. del Ray, Gene 97:173-182, 1991). We show that spri mutant cells do not hydrolyze p-nitrophenyl-1-D-glucoside or laminarin in a whole-cell assay for exo-1,3-13-glucanases. In addition to the absence of this enzymatic activity, sprl mutant spores exhibit reduced thermoresistance relative to isogenic wild-type spores. These observations are consistent with the notion that SPRI encodes a sporulation-specific exo-1,3-0-glucanase.In Saccharomyces cerevisiae, sporulation is initiated when a/a diploids are deprived of glucose and nitrogen. This complex pathway, which includes premeiotic DNA synthesis, high levels of genetic recombination, and two meiotic divisions, culminates in the formation of an ascus containing four haploid ascospores (reviewed in reference 11). Molecular and genetic analyses of this pathway are important because sporulation can serve as a model system for eukaryotic differentiation, i.e., for the coordination of a complex series of events that result in the formation of a new cell type. Furthermore, the process of recombination and meiosis is fundamental to eukaryotic biology.Genetic analysis has identified more than 30 complementation groups that are required for the completion of specific sporulation events (11,45); several of these genes have been cloned either by direct complementation of spo mutants, e.g., spoll (1)