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J Virol, April 1998, p. 3401-3406, Vol. 72, No. 4
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Molluscum Contagiosum Virus Topoisomerase:
Purification, Activities, and Response to Inhibitors
Young
Hwang,
Beibei
Wang, and
Frederic D.
Bushman*
The Salk Institute for Biological Studies, La
Jolla, California 92037
Received 22 October 1997/Accepted 17 December 1997
Molluscum contagiosum virus (MCV), the only member of the
Molluscipoxvirus genus, causes benign papules in healthy
people but disfiguring lesions in immunocompromised patients. The
sequence of MCV has been completed, revealing that MCV encodes a
probable type I topoisomerase enzyme. All poxviruses sequenced to date also encode type I topoisomerases, and in the case of vaccinia virus
the topoisomerase has been shown to be essential for replication. Thus,
inhibitors of the MCV topoisomerase might be useful as antiviral agents. We have cloned the gene for MCV topoisomerase, overexpressed and purified the protein, and begun to characterize its activities in
vitro. Like other eukaryotic type I topoisomerases, MCV topoisomerase can relax both positive and negative supercoils. An analysis of the
cleavage of plasmid and oligonucleotide substrates indicates that
cleavage by MCV topoisomerase is favored just 3' of the sequence 5'
(T/C)CCTT 3', resulting in formation of a covalent bond to the 3' T
residue, as with other poxvirus topoisomerases. We identified solution
conditions favorable for activity and measured the rate of formation
and decay of the covalent intermediate. MCV topoisomerase is sensitive
to inhibition by coumermycin A1 (50% inhibitory concentration, 32 µM) but insensitive to five other previously reported topoisomerase inhibitors. This work provides the point of departure for studies of
the mechanism of function of MCV topoisomerase and the development of
medically useful inhibitors.
*
Corresponding author. Mailing address: The Salk
Institute for Biological Studies, 10010 N. Torrey Pines Rd., La Jolla,
CA 92037. Phone: (619) 453-4100. Fax: (619) 554-0341. E-mail:
rick_bushman{at}qm.salk.edu.
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