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

Abstract

A Schizosaccharomyces pombe homolog of mammalian genes encoding G protein β 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. The gpb1 gene encodes 317 amino acids that show 47% homology with human Gβ1 and Gβ2 and 40% homology with Saccharomyces cerevisiae Gβ protein. Disruption of the gpb1 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% of gpb1-disrupted haploid pairs had undergone conjugation and sporulation, whereas only 3-5% of wild-type haploid pairs had done so. Overexpression of the gpb1 gene suppressed this facilitated conjugation and sporulation phenotype of gpb1-disrupted cells but did not cause any obvious effect in wild-type cells. Co-disruption of one of the two S. pombe Gα-subunit genes, gpa2, in the gpb1-disrupted cells did not change the accelerated conjugation and sporulation phenotype of the gpb1- cells. However, co-disruption of the ras1 gene abolished the gpb1- phenotype. These results suggest that Gpb1 is a negative regulator of conjugation and sporulation that apparently works upstream of Ras1 function in S. pombe. The possible relationship of Gpb1 to two previously identified, putative Gα proteins of S. pombe is discussed.