p130 is a tumor suppressor of the pocket protein family whose expression is posttranscriptionally regulated and largely G0 restricted. The mechanism of down-regulation of p130 expression in proliferating cells was investigated and results indicate that the decline of p130 expression as G0 cells reenter the cell cycle is due to a decrease in protein stability. In vitro polyubiquitination of p130 by SCF(Skp2) was specifically dependent on phosphorylation of p130 on Serine 672 (1). The retinoblastoma family of proteins including pRB, p107 and p130 undergoes cell cycle dependent phosphorylation during the mid-G1 to S phase transition. This phosphorylation is dependent upon the activity of cyclin D/cdk4. In contrast to pRB and p107, p130 is phosphorylated during G0 and the early G1 phase of the cell cycle. Also it is thought that p130, forming a complex with Rad50 through RINT-1, blocks telomerase-independent telomere lengthening in normal cells. Data indicates complementary roles for the Rb/E2F pathway in the control of telomere length (3).