Whether these cellular functions are active in cells prior to viral infection in vivo or whether they are activated during infection is currently being tested

Whether these cellular functions are active in cells prior to viral infection in vivo or whether they are activated during infection is currently being tested. ACKNOWLEDGMENTS This work was supported by Public Health Services grants (R37CA20260 from your National Cancer Institute and PO1NS35138 from your National Institute of Neurological Disorders and Stroke). We thank Robert Jordan for helpful discussions and suggestions, Amy Rosenberg for superb complex assistance, and Amy Francis, Jennifer Isler, and William Halford for critically reading the manuscript. REFERENCES 1. specific for erk-1 and -2) or iso-Olo (a structural isomer of Olo that does not inhibit cdk activity). The concentrations of Rosco and Olo required to inhibit cell cycle progression and viral replication in both HEL and Vero cells were related. Inhibition of viral replication was found not to become mediated by drug-induced cytotoxicity. Attempts to isolate Rosco- or Olo-resistant HSV mutants were unsuccessful, indicating that these drugs do not take action by inhibiting a single viral target. Viral DNA replication and build up of IE and early viral RNAs were inhibited in the presence of cell cycle-inhibitory concentrations of Tg Rosco or Olo. We consequently conclude that one or more cdks active from late G1 onward or inactive in nonneuronal cells are required for build up of HSV transcripts, viral DNA replication, and production of infectious computer virus. In mammalian cells, the nuclear environment varies substantially during each phase of the cell cycle. Thus, only S-phase nuclei consist of all the transcriptional, enzymatic, structural, and metabolic factors required for semiconservative DNA replication (12). To ensure the replication of their genomes, DNA-containing viruses have developed unique strategies to conquer the problems offered by a changing nuclear environment (12, 33). The simplest strategy is characteristic of the smallest DNA viruses, the parvoviruses, which replicate their genomes only when the infected cell progresses into the S phase (3, 12, 33). The polyomaviruses (including simian computer virus 40), on the other hand, induce infected cells to progress into the S phase (7, 12, 33). Therefore, these small DNA viruses are able to use cellular factors present or active in late G1 or early S as a consequence of either spontaneous or induced cell cycle progression. Although these replication strategies are highly successful, support of viral replication is limited to the people cells that are able to progress into the S phase. In contrast to these viruses, the alphaherpesviruses, such as herpes simplex virus (HSV), have adopted a strategy that permits genome replication in growth-arrested cells, including terminally differentiated, noncycling neurons, as well as with actively dividing SMER-3 cells. In this sense, HSV replication is definitely cell cycle independent. This does not imply, however, that a cellular function(s) associated with cell cycle progression is not required for HSV replication. Indeed, associations between HSV illness and cell cycle-related cellular functions are well recorded. Therefore, HSV replication is definitely blocked in the nonpermissive heat in five temperature-sensitive cell lines growth arrested in G0/G1 (55, 61). Moreover, HSV has long been known to replicate more efficiently in actively dividing than in growth-arrested cells of most types, and this enhancement of replication effectiveness is especially prominent for certain HSV strains with mutations in genes not absolutely required for viral replication (5, 10). For example, the replication impairment of ICP0? mutants can be complemented by cellular functions which are active during progression from G0 to the late G1/S phase of SMER-3 the cell cycle (5). Such complementation is definitely consistent with a model in which during wild-type computer virus illness, ICP0 substitutes for or induces a cellular activity normally indicated only in the G1 and early S phases of SMER-3 the cell cycle. In a similar vein, HSV mutants that do not communicate active thymidine kinase (TK) or ribonucleotide reductase are impaired for replication in growth-arrested G0/G1 cells but replicate to wild-type levels in growing cells, which communicate the cellular counterparts of these viral enzymes in late G1/S (18, 27). In the molecular level, cellular proteins normally indicated only in late G1 and S (proliferating cell nuclear antigen [PCNA], RP-A, DNA polymerase , and DNA ligase 1) or directly involved in cell cycle rules (pRb and p53) have been recognized in HSV DNA replication compartments of serum-starved cells, which are presumably arrested in G0/G1 (59). E2F DNA binding activity, cyclin-dependent kinase 2 (cdk-2) activity, and cyclin A protein, which are all specific for the late G1, S, or G2 phase of the cell cycle, have been reported to be induced during HSV illness of serum-starved cells (23, 25)..