J Virol, April 1998, p. 3107-3116, Vol. 72, No. 4
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
N. K. Koltzov Institute of Developmental Biology, Moscow, Russia1; Laboratory of Molecular Entomology and Baculovirology, The Institute of Physical and Chemical Research (RIKEN), Wako, Japan2; and Department of Entomology, University of California, Davis, California 956163
Received 21 October 1997/Accepted 12 December 1997
A DNA-binding protein (designated DBP) with an apparent molecular
mass of 38 kDa was purified to homogeneity from BmN cells (derived from
Bombyx mori) infected with the B. mori
nucleopolyhedrovirus (BmNPV). Six peptides obtained after digestion of
the isolated protein with Achromobacter protease I were
partially or completely sequenced. The determined amino acid sequences
indicated that DBP was encoded by an open reading frame (ORF16) located
at nucleotides (nt) 16189 to 17139 in the BmNPV genome (GenBank
accession no. L33180). This ORF (designated dbp) is a
homolog of Autographa californica multicapsid NPV ORF25,
whose product has not been identified. BmNPV DBP is predicted to
contain 317 amino acids (calculated molecular mass of 36.7 kDa) and to
have an isoelectric point of 7.8. DBP showed a tendency to
multimerization in the course of purification and was found to bind
preferentially to single-stranded DNA. When bound to oligonucleotides,
DBP protected them from hydrolysis by phage T4 DNA
polymerase-associated 3'
5' exonuclease. The sizes of the protected
fragments indicated that a binding site size for DBP is about 30 nt per
protein monomer. DBP, but not BmNPV LEF-3, was capable of unwinding
partial DNA duplexes in an in vitro system. This helix-destabilizing
ability is consistent with the prediction that DBP functions as a
single-stranded DNA binding protein in virus replication.
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