The Rlm1 transcription factor is a target of the cell wall integrity pathway. We report that an Δ mutant grown on a nonfermentable carbon source at low osmolarity forms cell groups in which a mother cell is surrounded by smaller "satellite-daughter" cells. Mother cells in these groups progressed through repeated rounds of cell division with normal rates of bud growth and genetic stability; however, these cells underwent precocious START relative to wild-type mothers. Thus, once activated, Rlm1 delays the transition from G to S, a mechanism we term the cell wall/START (CW/START) checkpoint. The Δ satellite-cell phenotype is suppressed by deletion of either, which encodes the kinase that activates Rlm1, or , which is also activated by Slt2; suggesting that Slt2 can have opposing roles in regulating the START transition. Consistent with an Rlm1-dependent CW/START checkpoint,Δ satellite daughters were unable to grow or divide further even after transfer to rich medium, but UV irradiation in G could partially rescue Δ satellite daughters in the next division. Indeed, after cytokinesis, these satellite daughters shrank rapidly, displayed amorphous actin staining, and became more permeable. As a working hypothesis, we propose that duplication of an "actin-organizing center" in late G may be required both to progress through START and to reestablish the actin cytoskeleton in daughter cells.
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