Differential regulation of adenovirus late transcriptional units by the products of early region.

Normal accumulation of adenoviral late mRNAs derived from the major late promoter, is mediated independently by either the ORF 6 or the ORF 3 product of E4. We have examined the role of E4 products in the expression of three late messages that are derived from outside the major late transcriptional unit: polypeptide IX mRNA, IVa2 mRNA, and messages from the E2 late promoter. We conclude that the late RNA accumulation phenotypes of E4 mutants can be broken down into two components. The effect on nuclear RNA accumulation, which is mediated independently by either the ORF 6 or ORF 3 products, is targeted to late messages derived from the major late transcriptional unit. A second small effect, that is mediated only by ORF 6, is needed for optimal accumulation of mRNA in the cytoplasm, and affects major late promoter derived messages as well as the message for polypeptide IX. The levels of IVa2 and E2 late messages are not reduced in cells infected with E4 negative mutants.