Herpes simplex virus infection blocks events in the G1 phase of the cell cycle

Infection of cells in G1 phase with herpes simplex virus (HSV) prevents the ir progression into S phase (de Bruyn Kops, A., and Knipe, D. M., 1988, Cel l 55, 857-868). We have examined G1-phase events in infected cells to deter mine whether this effect was the result of inhibition of G1 phase progressi on or of entry into S phase, We observed that HSV infection decreased pRb p hosphorylation and induced a new phosphorylated form of pRb. Furthermore, H SV infection prevented the normal G1 increases in cyclin D1 and D3 protein levels, and blocked the normal G1 appearance of new electrophoretic forms o f cdk2 and cdk4. Thus, HSV infection inhibits several events that normally occur in the cell cycle during G1 phase, arguing that the HSV-induced block in the cell cycle occurs in early to mid-G1 phase. (C) 2000 Academic Press .