FUNCTIONAL EXPRESSION AND MOLECULAR CHARACTERIZATION OF ATUBC2-1, A NOVEL UBIQUITIN-CONJUGATING ENZYME (E2) FROM ARABIDOPSIS-THALIANA

The first member of a novel subfamily of ubiquitin-conjugating E2-prot eins was cloned from a cDNA library of Arabidopsis thaliana. Genomic b lots indicate that this gene family (AtUBC2) consists of two members a nd is distinct from AtUBC1, the only other E2 enzyme known from this s pecies to date (M.L. Sullivan and R.D. Vierstra, Proc. Natl. Acad. Sci . USA 86 (1989) 9861-9865). The cDNA sequence of AtUBC2-1 extends over 794 bp which would encode a protein of 161 amino acids and a calculat ed molecular mass of 18.25 kDa. The protein encoded by AtUBC2-1 is sho wn to accept I-125-ubiquitin from wheat E1 enzymes, when expressed fro m Escherichia coli hosts as fusion protein carrying N-terminal extensi ons. It is deubiquitinated in the presence of lysine and, by these cri teria, is considered a functional E2 enzyme.