Abstract: A method for isolating and purifying novel species of E2 ubiquitin-carrier protein, designated E2-F1, is disclosed. A method for preparing enzymatically active fragments of E2-F1 enzyme is also disclosed. The use of purified E2-F1 to produce antibodies is also disclosed. The use of such E2-F1-specific antibodies to detect the presence of E2-F1 in a biological sample, and to inhibit protein degradation are also disclosed. Recombinant DNA molecules which code for E2-F1, and recombinant hosts and vectors which contain E2-F1 coding sequences are also disclosed. The use of such recombinant hosts and vectors to produce E2-F1 protein is also disclosed. The use of purified E2-F1 to identify and to isolate E3 enzyme is also disclosed. Methods for screening substances for the ability to inhibit E2-F1 enzyme activity are also disclosed.