A genomics approach to identifying G1 regulators.
Jian Zou, Michael Constanzo, Helena Friesen, Brenda Andrews
Molecular and Medical Genetics, University of Toronto, 1 King's College
Cr., Toronto, ON M5S 1A8, Canada
Entry into the mitotic cell cycle (passage through START) requires a
burst of transcription in late G1 phase of the cell cycle. This
transcription is mediated by the heterodimeric transcription factor, SBF
or MBF. Although SBF and MBF appear genetically redundant, we, and
others, have evidence that they are activated and regulated by different
gene products. To identify regulators specific for SCB or MCB-driven
gene expression we used Synthetic Genetic Array (SGA) analysis to 1)
introduce MCB and SCB-lacZ reporter genes into an array of
5000 yeast deletion mutants and 2) screen a subset of gene-deletion
strains for synthetic lethal interactions with the G1 regulators,
SWI4, SWI6, STB1, and MBP1. We identified
approximately 60 mutants that showed a defect in SCB or
MCB reporter gene expression. In the course of these analyses we
noticed that a number of previously identified synthetic lethal
interactions did not appear in these screens; for example the swi4
swi6 double mutants were viable. These data suggested that
synthetic lethal interactions between genes encoding a variety of G1
regulators were being suppressed in the strain background of the
deletion set. We have now made a genetic background (ssd1-d
allele linked to a selectable marker) for use in SGA screens to look for
genetic interactions with G1 regulators. We are currently doing SGA
screens to compare the synthetic lethal profiles of various mutants in
SSD1-v and ssd1-d strain backgrounds.
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