A yeast gene required for the G1-to-S transition encodes a protein containing an A-kinase target site and GTPase domain.

A new temperature-sensitive mutant of Saccharomyces cerevisiae, gst1 (G1-to-S transition) was isolated. At nonpermissive temperature the mutant cells with large buds accumulated and DNA synthesis was substantially arrested. From the reciprocal experiment of temperature-shift and mating-factor treatment, it was shown that the execution point was post 'START'. This suggested that the mutation affected the G1-to-S phase transition in the cell cycle. A DNA clone complementing the gst1-1 mutation was isolated from a yeast gene library, and gst1 was mapped in chr4R, by Southern blotting of cloned sequence to the individual yeast chromosome DNA by OFAGE system and by genetic analysis. The gene product was tentatively assigned from DNA sequencing analysis, as a protein of mol. wt 76,565 which contained consensus sequences for a target site of cAMP-dependent protein kinase(s) and for GTPase with extensive homology to polypeptide chain elongation factor EF1 alpha.