Human cytomegalovirus UL69 protein induces cells to accumulate in G(1) phase of the cell cycle

Earlier studies have revealed that human cytomegalovirus rapidly inhibits t he growth of fibroblasts, blocking cell cycle progression at multiple point s, including the G(1)-to-S-phase transition. The present study demonstrates that the UL69 protein, a virus-encoded constituent of the virion, is able to arrest cell cycle progression when introduced into uninfected cells, Exp ression of the UL69 protein causes U2 OS cells and primary human fibroblast s to accumulate within the G(1) compartment of the cell cycle, and serum fa ils to induce the progression of quiescent human fibroblasts into the S pha se when the protein is present. Therefore, the UL69 protein is at least par tially responsible for the cell cycle block that is instituted after infect ion of permissive cells with human cytomegalovirus.