Synthesis of herpes simplex virus DNA in a soluble nuclear extract

The ATP requirements of adenovirus type 5 DNA replication and cellular DNA replication

Several in vitro DNA replication systems were employed to characterize the ATP dependency of adenovirus type 5 (Ad5) DNA replication. Ad5 DNA synthesis in isolated nuclei, representing the elongation of nascent DNA chains, was slightly ATP dependent. Reduction of the ATP concentration from the optimum (8 mM) to the endogenous value (0.16 microM) reduced Ad5 DNA replication only to 70%. No change in the pattern of replication was observed as indicated by the analysis of replicative intermediates using agarose gel electrophoresis. ATP could be replaced by dATP, but not by GTP or other nucleoside triphosphates. By contrast, cellular DNA replication in isolated nuclei from HeLa cells was reduced to 12% by the omission of ATP. These differences could not be explained by different ATP pools or by effects of ATP on dNTP pools. Cellular DNA replication in contrast to viral DNA replication was sensitive to low concentrations of adenosine 5'-O-(3-thiotriphosphate). Inhibition by this ATP analog was competitive with ATP (Ki = 0.4 mM). Adenovirus DNA replication by DNA-free nuclear extracts, representing initiation plus elongation (Challberg and Kelly, Proc. Nat. Acad. Sci. USA 76, 655-659, 1979), exhibited a nearly absolute requirement for ATP. ATP could be substituted not only by dATP, but also by GTP and dGTP and to a lesser extent by pyrimidine triphosphates. Similar results were found when the formation of a covalent complex between dCTP and the precursor terminal protein was studied. This reaction is essential for the initiation of Ad5 DNA replication. The results indicate that different ATP-requiring functions are employed during the initiation and elongation stages of adenovirus DNA replication.

Replication of herpes simplex virus type I DNA in permeabilized infected cells

Herpes simplex type 1 (HSV)-infected Vero cells can be permeabilized by a combination of hypotonic shock and a mild emulsifier, gum arabic. Permeabilized cells will incorporate triphosphate precursors into viral and host DNA in vitro in ratios similar to those seen in vivo. This reaction is ATP-dependent and is shown to be replicative by the single strand density shift of DNA synthesized in the presence of BrdUTP. The product is heterogeneous in size, and contains a significant proportion of rapidly sedimenting forms and of unit size (55S) viral DNA. The presence of polyamines and EGTA (a specific chelator of Ca2+ ions) in the labeling medium is shown to be necessary to maintain the integrity of the replicating DNA. The average size of newly synthesized single strands, however, is smaller than seen in vivo. The reaction is sensitive to phosphonoacetic acid added at the time of labeling, at concentrations which inhibit in vivo synthesis only after one hour of pre-exposure. These properties make permeabilized cell monolayers an attractive system for the study of HSV DNA replication.