The Kluyveromyces lactis heterotrimeric G protein is a canonical G alpha beta gamma complex; however, in contrast to Saccharomyces cerevisiae, where the G gamma subunit is essential for mating, disruption of the KlG gamma gene yielded cells with almost intact mating capacity. Expression of a nonfarnesylated G gamma, which behaves as a dominant-negative in S. cerevisiae, did not affect mating in wild-type and Delta G gamma cells of K. lactis. In contrast to the moderate sterility shown by the single Delta KlG alpha, the double Delta KlG alpha Delta KlG gamma mutant displayed full sterility. A partial sterile phenotype of the Delta KlG gamma mutant was obtained in conditions where the KlG beta subunit interacted defectively with the G alpha subunit. The addition of a CCAAX motif to the C-end of KlG beta, partially suppressed the lack of both KlG alpha and KlG gamma subunits. In cells lacking KlG gamma, the KlG beta subunit cofractionated with KlG alpha in the plasma membrane, but in the Delta KlG alpha Delta KlG gamma strain was located in the cytosol. When the KlG beta-KlG alpha interaction was affected in the Delta KlG gamma mutant, most KlG beta fractionated to the cytosol. In contrast to the generic model of G-protein function, the G beta subunit of K. lactis has the capacity to attach to the membrane and to activate mating effectors in absence of the G gamma subunit.
Última actualización: 21/10/2016