A first exon-encoded domain of E1A sufficient for posttranslational modification, nuclear-localization, and induction of adenovirus E3 promoter expression in Xenopus oocytes.

The purified Escherichia coli-expressed human subgroup C adenovirus E1A 13S mRNA product induces expression from the adenovirus type 5 E3 promoter when injected into Xenopus oocytes. In the present communication, the E. coli-expressed E1A 13S and 12S mRNA products are shown to undergo a posttranslational modification in microinjected Xenopus oocytes, which causes a 2- to 4-kDa increase in apparent molecular size, identical to that occurring in HeLa cells expressing the E1A gene. The E. coli-expressed E1A proteins are similarly modified in vitro in a soluble rabbit reticulocyte lysate. The modified form of the E1A proteins preferentially localizes to the oocyte nucleus following cytoplasmic microinjection. The use of various deleted forms of E1A protein synthesized in E. coli shows that a first exon-encoded domain of E1A, residing between amino acid residues 23 and 120, is sufficient for the posttranslational modification and nuclear localization of E1A and also for the trans-activation of the E3 promoter by E1A in Xenopus oocytes. These results suggest that the posttranslational modification of E1A protein may be important for its function.