MUTATIONAL ANALYSIS OF A PREDICTED ZINC-BINDING MOTIF IN THE 26-KILODALTON PROTEIN ENCODED BY THE VACCINIA VIRUS A2L-GENE - CORRELATION OF ZINC-BINDING WITH LATE TRANSCRIPTIONAL TRANSACTIVATION ACTIVITY

Transient transfection assays indicated that A2L is one of three vacci nia virus intermediate genes that are required for the transcriptional transactivation of viral late genes. We have expressed the A2L open r eading frame in Escherichia coli and shown by blotting experiments tha t the 26-kDa protein binds zinc, a property predicted by the presence of a CX2CX13CX2C zinc finger motif. The specificity for zinc binding w as demonstrated by competition with other metals. The role of the sequ ence motif in zinc binding was established by analysis of a series of mutations, including truncations and conservative single amino acid su bstitutions. Mutations that reduced zinc binding in vitro prevented th e ability of A2L to transactivate late genes in vivo.