Separation of the functions controlled by adenovirus 2 lp+ locus

The adenovirus lp+ locus is located within early region E1b (map position 4.5-11.2) and codes for a 19-kDa tumor antigen (175R). Genetic analysis of the viral mutants that map within this region indicates that the lp+ locus controls multiple functions in cell transformation and in productive viral infection. Viral mutants mapping within the lp+ locus produce wt-like cytopathic effect (cyt+) or a cytocidal (cyt) effect. Earlier results have shown that many of the viral mutants that produce cyt phenotype in infected cells are transformation defective. In the present studies we show that one of the cyt mutants, cyt 106 which has a single amino acid substitution at position 20 transforms the established rat embryo cell line, CREF, at somewhat reduced frequency. Nonetheless, the cyt106-transformed cells appear to be fully transformed when compared with Ad2 wild type transformed cells. Unlike most other cyt mutants, cyt 106 is dominant over Ad2 wild type in mixed infections as judged by the plaque morphology in infective center assays and by the cytopathic effect. The dominant nature of the mutation may contribute to the observed transformation characteristics. Earlier we have shown that a cytocidal mutant, dl250 is partially defective in viral DNA synthesis in human KB cells. Now we show that two other cyt mutants cyt 5 (with a chain termination mutation near the C terminus) and cyt 6 (with a single amino acid substitution at position 44) are also partially defective in viral DNA synthesis in human KB cells. In contrast to these mutants, mutant cyt 106 induces normal replication of viral DNA. The DNA replication defect in mutants cyt 5 and 6 can be complemented in trans in 293 cells that constitutively express the 175R T antigen. Our results also indicate that a domain of this protein around the 44th amino acid is important for efficient viral DNA synthesis in KB cells.