p27fs177 is highly unstable also in primary rat fibroblasts. (a) RNF mut cells progress through the cell cycle as RNF wt cells. FACS analysis of DNA content. (b) CHX treatment on exponentially growing RNFs. The asterisk indicates a non-specific band. (c) Endogenous p27fs177 is in part degraded by the proteasome. RNFs were treated with CHX and epoxomycin (+) or DMSO (-) for the indicated times. Left: Endogenous p27fs177 is so unstable that often can be detected only in the presence of proteasome inhibitors such as EPOX. Right: p27fs177 is actively degraded not only in exponentially growing (Exp) RNF mut cells but also in serum-starved cells (SS) and is stabilized by treatment with EPOX.