Mapping of a phosphorylation site in the 176R (19 kDa) early region 1B protein of human adenovirus type 5

Abstract

The 176-residue (176R) early region 1 B (El B) protein of human adenovirus type 5 (Ad5) was shown to be phosphorylated at serine in lytically infected KB cells at a level estimated to be about one phosphate group per 28 176R molecules. Through the analysis of peptides generated by cleavage with cyanogen bromide and Staphylococcus aureus V-8 protease the phosphorylation site was mapped to Ser-164. Using site-directed mutagenesis, a mutant was produced in which the codon for Ser-164 was changed to that of asparagine while leaving the coding sequence for the overlapping 496R protein unchanged. This virus, which replicated well on human KB cells, produced normal levels of 176R, but in an unphosphorylated form. The mutant transformed baby rat kidney cells in cooperation with El A at an efficiency about one-half that obtained with wt E1 B. These data therefore gave little indication that phosphorylation is essential for the function of 176R.