UBC11 is the Saccharomyces cerevisiae gene that is most similar in sequence to E2-C, a ubiquitin carrier protein required for the destruction of mitotic cyclins and proteins that maintain sister chromatid cohesion in animal cells and in Schizosaccharomyces pombe. We have disrupted the UBC11 gene and found it is not essential for yeast cell viability even when combined with deletion of UBC4, a gene that has also been implicated in mitotic cyclin destruction. Ubc11p does not ubiquitinate cyclin B in clam cell-free extracts in vitro and the destruction of Clb2p is not impaired in extracts prepared from delta ubc11 or delta ubc4 delta ubc11 cells. These results suggest Ubc4p and Ubc11p together are not essential for mitotic cyclin destruction in S. cerevisiae and we can find no evidence to suggest that Ubc11p is the true functional homologue of E2-C.