The de-ubiquitinating enzyme Unp interacts with the retinoblastoma protein

The ubiquitin pathway is involved in the proteolytic turnover of many short -lived cellular regulatory proteins. Since selective degradation of substra tes of this system requires the covalent attachment of a polyubiquitin chai n to the substrates, degradation could be counteracted by de-ubiquitinating enzymes (or isopeptidases) which selectively remove the polyubiquitin chai n. Unp is a human isopeptidase with still poorly understood biological func tions. Here, we show that cellular Unp specifically interacts with the reti noblastoma gene product (pRb).