Mutations of the Precursor to the Terminal Protein of Adenovirus Serotypes 2 and 5

Using a series of transient expression plasmids and adenovirus-specific DNA replication assays for both initiation and elongation, we measured the relative activities of mutant polypeptides of the precursor to the terminal protein (pTP) in vitro. Mutations that removed two to six amino acids of the amino terminus gradually decreased pTP activity; a deletion of 18 amino acids was completely inactive. Replacement of cysteine at residue 8 with a serine had little effect on pTP activity. Two amino-terminal in-frame linker insertion mutant polypeptides previously characterized in vivo as either replication defective or temperature sensitive had considerable activity at the permissive temperature in vitro. For one mutant pTP with a temperature-sensitive phenotype in vivo, elongation activity was decreased more than initiation in vitro, suggesting a role for this protein after the initiation step. Replacement mutations of serine 580, the site of covalent attachment of dCTP, completely abolished pTP function for both initiation and elongation.