The G protein β subunit Gpb1 ofSchizosaccharomyces pombe is a negative regulator of sexual development

ASchizosaccharomyces pombe homolog of mammalian genes encoding G proteinβ subunits,gpb1 ⁺, was cloned by the polymerase chain reaction using primer pairs that correspond to sequences conserved in several Gβ genes of other species followed by screening of genomic and cDNA libraries. Thegpb1 gene encodes 317 amino acids that show 47% homology with human Gβ ₁ and Gβ ₂ and 40% homology withSaccharomyces cerevisiae Gβ protein. Disruption of thegpb1 gene indicated that this gene is not required for vegetative cell growth. However,gpb1-disrupted haploid cells mated and sporulated faster than wild-type cells, both in sporulation (MEA) and in complex medium (YE): when examined 23 h after transfer to sporulation medium, 35% ofgpb1-disrupted haploid pairs had undergone conjugation and sporulation, whereas only 3–5% of wild-type haploid pairs had done so. Overexpression of thegpb1 gene suppressed this facilitated conjugation and sporulation phenotype ofgpb1-disrupted cells but did not cause any obvious effect in wild-type cells. Co-disruption of one of the twoS. pombe Gα-subunit genes,gpa2, in thegpb1-disrupted cells did not change the accelerated conjugation and sporulation phenotype of thegpb1 ^? cells. However, co-disruption of theras1 gene abolished thegpb1 ^? phenotype. These results suggest that Gpbl is a negative regulator of conjugation and sporulation that apparently works upstream of Ras1 function inS. pombe. The possible relationship of Gpbl to two previously identified, putative Gα proteins ofS. pombe is discussed.