MOUSE ADENOVIRUS TYPE-1 EARLY REGION 1A IS DISPENSABLE FOR GROWTH IN CULTURED FIBROBLASTS

Mouse adenovirus type 1 (MAV-1) mutants with deletions of conserved re gions of early region 1A (E1A) or with point mutations that eliminate translation of E1A were used to determine the role of E1A in MAV-1 rep lication. MAV-1 E1A mutants expressing no E1A protein grew to titers c omparable to wild-type MAV-1 titers on mouse fibroblasts (3T6 fibrobla sts and fibroblasts derived from Rb+/+, Rb+/-, and Rb-/- transgenic em bryos). To test the hypothesis that E1A could induce a quiescent cell to reenter the cell cycle, fibroblasts were serum starved to stop DNA replication and cellular replication and then infected,vith the E1A mu tant and wild-type viruses. All grew to equivalent titers. Steady-stat e levels of MAV-1 early mRNAs (E1A, E1B, E2, E3, and E4) from 3T6 cell s infected with wild-type or E1A mutant virus were examined by Norther n analysis. Steady-state levels of mRNAs from the mutant-infected cell s were comparable to or greater than the levels found in wild-type vir us infections for most of the early regions and for two late genes. Th e E2 mRNA levels were slightly reduced in all mutant infections relati ve to wild-type infections. E1A mRNA was not detected from infections, vith the MAV-1 E1A null mutant, pmE109, or from infections with simila r MAV-1 E1A null mutants, pmE112 and pmE113. The implications for the lack of a requirement of E1A in cell culture are discussed.