Cloning of human ubiquitin conjugating enzymes UbcH 6 and UbcH 7 ( E 2 F1 ) and characterization of their interaction with E 6 AP and RSP 5 . ^^^ In this paper , we describe the isolation of two human E2s , designated as UbcH 6 and UbcH 7 , that in addition to UbcH 5 can interact with E 6 AP . ^^^