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Journal of Virology, January 2000, p. 245-253, Vol. 74, No. 1
Department of Medical Microbiology and
Immunology, Texas A&M University System Health Science Center,
College Station, Texas 77843-1114
Received 7 June 1999/Accepted 4 October 1999
The E1 protein of bovine papillomavirus (BPV) is a site-specific
DNA binding protein that recognizes an 18-bp inverted repeat element in
the viral origin of replication. Sequence-specific DNA binding function
maps to the region from approximately amino acids 140 to 300, and
isolated polypeptides containing this region have been shown to retain
origin binding in vitro. To investigate the sequence and structural
characteristics which contribute to sequence-specific binding, the
primary sequence of this region was examined for conserved features.
The BPV E1 DNA binding domain (E1DBD) contains three major hydrophilic
domains (HR1, amino acids 179-191; HR2, amino acids 218 to 230; and
HR3, amino acids 241 to 252), of which only HR1 and HR3 are conserved
among papillomavirus E1 proteins. E1DBD proteins with lysine-to-alanine
mutations in HR1 and HR3 were severely impaired for DNA binding
function in vitro, while a lysine-to-alanine mutation in HR2 had a
minimal effect on DNA binding. Mutation of adjacent threonine residues in HR1 (T187 and T188) revealed that these two amino acids made drastically different contributions to DNA binding, with the T187 mutant being severely defective for origin binding whereas the T188
mutant was only mildly affected. Helical wheel projections of HR1
predict that T187 is on the same helical face as the critical lysine
residues whereas T188 is on the opposing face, which is consistent with
their respective contributions to DNA binding activity. To examine E1
binding in vivo, a yeast one-hybrid system was developed. Both
full-length E1 and the E1DBD polypeptide were capable of specifically
interacting with the E1 binding site in the context of the yeast
genome, and HR1 was also critical for this in vivo interaction.
Overall, our results indicate that HR1 is essential for origin binding
by E1, and the features and properties of HR1 suggest that it may be
part of a recognition sequence that mediates specific E1-nucleotide contacts.
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Identification of a Short, Hydrophilic Amino Acid Sequence
Critical for Origin Recognition by the Bovine Papillomavirus E1
Protein
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Corresponding author. Mailing address: Department of
Medical Microbiology and Immunology, Texas A&M University System Health Science Center, College Station, TX 77843-1114. Phone: (409) 845-5207. Fax: (409) 845-3479. E-mail: v-wilson{at}tamu.edu.
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