FUNCTIONAL-ANALYSIS OF HUMAN CYTOMEGALOVIRUS POLYMERASE ACCESSORY PROTEIN

The human cytomegalovirus (HCMV) UL44 gene product, polymerase accesso ry protein, was cloned and expressed in Escherichia coli as a 53 000 M W protein. The activity of HCMV DNA polymerase (Pol) alone and Pol/UL4 4 complex was evaluated in Pol assays designed specifically to elucida te Pol/UL44 interactions. Addition of UL44 to HCMV Pol with primed, si ngle-stranded DNA resulted in increased incorporation of nucleotides i nto DNA, which was correlated with enhanced enzyme processivity. Sever al deletion mutants which span the UL44 sequence were constructed and examined for the ability to stimulate Pol activity and to bind double- stranded DNA. The functional domains of UL44 protein were determined t o reside within the N-terminal 309 amino acids of the wild type sequen ce, since deletions within this region resulted in loss of DNA binding and the ability to stimulate Pol. Deletion of C-terminal amino acids 310-433 had no effect on the ability of UL44 protein to increase the p rocessivity of HCMV DNA Pol.