Association of Type I DNA Topoisomerase with Herpes Simplex Virus

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Abstract
A topoisomerase activity is associated with herpes simplex virus type 1. The enzyme was recovered from purified virions which were disrupted with 6 M guanidine-HCl followed by renatuation of extracted proteins. The virion activity is classified as a type I topoisomerase because the linking number of a unique DNA topoisomer is altered in steps of one; ATP and MgCl2 are not required for activity; the enzyme can be trapped in a covalent complex with DNA; and the covalent linkage to DNA is through a 3'' phosphoryl bond. It is strongly indicated that the topoisomerase is external to the nucleocapsid: the activity was released by treatment of intact virions with NP40, and subsequent washing steps extracted most residual activity; when guanidine extracts were prepared from nucleocapsids, topoisomerase activity was not detectable; and DNA within the virion did not appear to contain covalently attached proteins with properties similar to topoisomerases. Thus, the enzyme appears to be a component of the envelope or tegument structure of the virion.

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