A family of structurally related RING finger proteins interacts specifically with the ubiquitin-conjugating enzyme UbcM4

The ubiquitin-conjugating enzyme UbcM4 was previously shown to be necessary for normal mouse development. As a first step in identifying target protei ns or proteins involved in the specificity of UbcM4-mediated ubiquitylation , we have isolated seven cDNAs encoding proteins that specifically interact with UbcM4 but with none of the other Ubcs tested. This interaction was ob served in yeast as well as in mammalian cells. With one exception, all UbcM 4-interacting proteins (UIPs) belong to a family of proteins that contain a RING finger motif. As they are structurally related to RING finger protein s that have recently been shown to play an essential role in protein ubiqui tylation and degradation, the possibility is discussed that UIPs are involv ed in the specific recognition of substrate proteins of UbcM4. (C) 1999 Fed eration of European Biochemical Societies.