Expression of p60v-src in Saccharomyces cerevisiae results in elevation of p34CDC28 kinase activity and release of the dependence of DNA replication on mitosis.

Expression of the oncogenic protein tyrosine kinase p60v-src in the yeast Saccharomyces cerevisiae has been shown to result in rapid cell death (J. S. Brugge, G. Jarosik, J. Andersen, A. Queral-Lustig, M. Fedor-Chaiken, and J. R. Broach, Mol. Cell. Biol. 7:2180-2187, 1987). Work described here demonstrates that v-Src expression results in accumulation of large-budded cells and a nuclear division block without blocking cytokinesis. Flow-cytometric analysis indicates that the DNA content of these cells is elevated beyond the G2 DNA content, and genetic studies indicate that v-Src expression causes aneuploidy. The activity of Cdc28 kinase, which controls the G1/S and G2/M transitions in S. cerevisiae, increases during galactose induction in a Src+ strain but not in an isogenic Src- strain. These observations indicate that v-Src expression disrupts p34CDC28 kinase regulation, allowing DNA replication to proceed in the absence of a prior mitotic event.