quiescence embryonic development fate senescence G0' response to DNA damage protein degradation stability G1-S transition pathogenesis immunoreactivity DNA nucleotide-excision repair s phase conjugation catabolism oncogenesis DNA damage recognition embryogenesis g1 phase regulation of signal transduction RNA localization amplify distribution relaxation cell survival transformation proteolysis assemble death maturation drug resistance proliferation mitogenesis apoptosis accumulation differentiation MDM2 TP53