The two idiomorphic alleles called mat+ and mat-, which control the mating types in Podospora anserina, have been cloned. Mat+ and mat- encompass 3.8 kb and 4.7 kb respectively, of unrelated DNA sequences flanked by common sequences. Subcloning allowed the identification and localization in each locus of the gene that controls fertilization, probably by determining the mating type. The mat+ gene, called FPR1, encodes a protein with a potential DNA-binding HMG domain. The presence of this motif suggests that the FPR1 polypeptide may act as a transcriptional factor. The mat- gene called FMR1 encodes a protein containing a motif that is also found in proteins controlling mating functions in Saccharomyces cerevisiae and Neurospora crassa. The role of this motif has not yet been established. Unlike the mat+ locus, where the FPR1 gene seems to represent the major information, the mat- locus contains information necessary for the post-fertilization steps of the sexual cycle besides the FMR1 gene.