Previous Article | Next Article ![]()
J. Virol., 06 1995, 3789-3798, Vol 69, No. 6
R Mendoza, L Gandhi and MR Botchan
The E1 protein encoded by bovine papillomavirus type 1 (BPV-1) is required
for viral DNA replication, and it binds site specifically to an A/T-rich
palindromic sequence within the viral origin of replication. The protein is
targeted to this site through cooperative interactions and binding with the
virus-encoded E2 protein. To explore the nature of the E1 binding site, we
inserted a series of homologous DNA linkers at the center of dyad symmetry
within the E1 recognition palindrome. The effects of these modifications
indicated that the E1 recognition palindrome can be separated into
functional half sites. The series of insertions manifest a phasing
relationship with respect to the wild-type BPV-1 genome in that greater
biological activity was measured when full integral turns of the DNA helix
separated the palindrome than when the separations were half-turns. This
phasing pattern of activity was observed to occur in a variety of
biological phenotypes, including transformation efficiency, stable plasmid
copy number in cell lines established from pooled foci, and transient
replication of full-length viral genomes. For replication reporter
constructs where E1 and E2 are supplied in trans by the respective
expression vectors, distance between the half sites seems to play a major
role, yet the phasing relationships are measurable. DNase I protection
studies showed that E1 bound very poorly to the construct containing a 5-bp
linker, and binding was close to the wild-type level for the 10-bp
insertion, consistent with a requirement for a phasing function between
half sites with a modulus of 10 bp. Binding to the 15- and 20-bp insertion
mutants was weak, but only for the 20-bp insertions was protection over
both halves of the palindrome measurable. As it had been previously
reported that the 18-bp palindrome contains sufficient nucleotide sequence
information for E1 binding, we speculate that a minimal E1 recognition
motif is presented in each half site. A comparison between this sequence
and that of an upstream region that also binds E1 (the E2RE1 region)
revealed a common pentanucleotide motif of APyAAPy. Mutants with
substitutions of the ATAAT elements within E2RE1 failed to bind E1 protein.
We present models for how repeats of the pentanucleotide sequence may
coordinate E1 binding at the dyad symmetry axis of the origin and compare
the DNA sequence organization of BPV-1 with those of the simian virus 40
and polyomaviruses at their origins of DNA replication.
Copyright © 1995, American Society for Microbiology
E1 recognition sequences in the bovine papillomavirus type 1 origin of DNA replication: interaction between half sites of the inverted repeats
Department of Molecular and Cell Biology, University of California, Berkeley 94720-3204, USA.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»