THE G-PROTEIN BETA-SUBUNIT GPB1 OF SCHIZOSACCHAROMYCES-POMBE IS A NEGATIVE REGULATOR OF SEXUAL DEVELOPMENT

A Schizosaccharomyces pombe homolog of mammalian genes encoding G prot ein beta subunits, gpbl(+), was cloned by the polymerase chain reactio n using primer pairs that correspond to sequences conserved in several G beta genes of other species followed by screening of genomic and cD NA libraries. The gpb1 gene encodes 317 amino acids that show 47% homo logy with human G beta(1) and G beta(2) and 40% homology with Saccharo myces cerevisiae G beta protein. Disruption of the gpb1 gene indicated that this gene is not required for vegetative cell growth. However, g pb1-disrupted haploid cells mated and sporulated faster than wild-type cells, both in sporulation (MEA) and in complex medium (YE): when exa mined 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 gp bl gene suppressed this facilitated conjugation and sporulation phenot ype of gpb1-disrupted cells but did not cause any obvious effect in wi ld-type cells. Go-disruption of one of the two S. pombe G alpha-subuni t genes, gpa2, in the gpb1-disrupted cells did not change the accelera ted conjugation and sporulation phenotype of the gpb1(-) cells. Howeve r, co-disruption of the ras1 gene abolished the gpb1(-) phenotype. The se results suggest that Gpb1 is a negative regulator of conjugation an d sporulation that apparently works upstream of Ras1 function in S. po mbe. The possible relationship of Gpb1 to two previously identified, p utative G alpha proteins of S. pombe is discussed.