SLG1 plays a role during G1 in the decision to enter or exit the cell cycle

Saccharomyces cerevisiae cells decide to divide during G1. If nutrients are abundant, cells pass through START and coordinately undergo DNA replication, bud emergence, and spindle pole body duplication. Phenotypic analysis of the slg1Δ mutant revealed that this mutation uncouples post-START events. At the nonpermissive temperature, slg1Δ cells that have undergone bud emergence but not DNA replication or SPB duplication accumulate. Furthermore, while wild-type cells arrest in G0 when starved, the slg1Δ mutant fails to arrest at this point; instead, cells with small buds accumulate. The slg1Δ mutation displayed genetic interactions with cdc34, which encodes a regulator of exit from G1. This is consistent with a role of SLG1 in G1 regulation. Epitope-tagged Slg1p cofractionated with the plasma membrane, suggesting that Slg1p may function by integrating external cues and relaying them to the interior of the cell. We propose that SLG1 plays a regulatory role in bud emergence or stationary phase.