PML and COP1--two proteins with much in common

The recent discovery that the RING-finger domain is involved in mediating ubiquitin transfer from ubiquitin-conjugating enzymes to substrates have highlighted the importance of protein degradation through the ubiquitin-proteasome pathway in the regulation of different cellular processes. Two RING-finger-containing proteins, the promyelocytic leukemia protein (PML) from mammals and the constitutive photomorphogenic protein (COP1) from plants, show conspicuous similarities in their cellular distribution, dynamics and structure, indicating that they share a related function. Comparison of these two proteins suggests that they are involved in regulating the targeting of nuclear proteins to specific nuclear compartments for degradation through the ubiquitin-proteasome pathway.