Codon insertion mutants of the adenovirus terminal protein

A series of codon insertion mutants was isolated following restriction site-directed linker insertion mutagenesis of the open reading frame for the type 5 adenovirus terminal protein precursor. The conditionally lethal mutant H5sub100 bears an insertion mutation upstream of the first AUG in the reading frame, fails to replicate its DNA under nonpermissive conditions, and was assigned to the terminal protein complementation group. These data establish that terminal protein is an essential polypeptide required for DNA replication in vivo and indicate that the NH2-terminal region of the precursor is encoded in an upstream mRNA leader. The extended eclipse period of the viral replication cycle in H5in179-infected cells is probably a consequence of delayed onset of DNA replication. Analysis of DNA replication in coinfections with wild-type virus shows that the in179 mutation has cis and trans effects. The trans-dominant, negative-complementing in179 terminal protein precursor inhibits wild-type DNA replication in a dose-dependent manner. Replication of parental in179 templates is not stimulated by an excess of coinfecting wild-type virus, indicating that the mutant terminal protein covalently bound to the in179 template in some way interferes with the replication of that template. The implications of these results for the structure and function of the terminal protein are discussed.