PEST, proteolytic signal-containing nuclear protein family
PCNP is a PEST-containing nuclear protein that is ubiquitinated by NIRF, a Np95/ICBP90-like RING finger protein. PEST sequences, which are rich in proline (P), glutamic acid (E), serine (S) and threonine (T), are found in a number of short-lived proteins, such as transcription factors and cell cycle-associated proteins. Their function is generally controlled by proteolysis, mostly via ubiquitin-mediated degradation. Thus, NIRF and PCNP are a ubiquitin ligase and its substrate, respectively, that may constitute a novel signalling pathway with some relation to cell proliferation.