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J. Biol. Chem., Vol. 276, Issue 19, 16123-16136, May 11, 2001
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From the Department of Human Biological Chemistry and Genetics, The
University of Texas Medical Branch, Galveston, Texas 77555-1053
Interactions between rat polymerase
Energetics and Specificity of Rat DNA Polymerase
Interactions
with Template-primer and Gapped DNA Substrates*
(pol
)
and the template-primer, as well as gapped DNAs, were studied using the
quantitative fluorescence titration technique. Stoichiometries of rat
pol
complexes with DNA substrates are much higher than
stoichiometries predicted by the structures of co-crystals. The data
can be understood in the context of the two single-stranded
(ss)DNA-binding modes of the enzyme, the (pol
)16
and (pol
)5 binding modes, which differ by the number of
nucleotides occluded by the protein. The 8-kDa domain of the enzyme
engages the double-stranded (ds)DNA downstream from the primer, while
the 31-kDa domain has similar affinity for the ss-ds DNA junction and
the dsDNA. The affinity of rat pol
for the gapped DNA is not
affected by the size of the gap. The results indicate a plausible
model for recognition of the gapped DNA by rat pol
. The enzyme
binds the ss-ds DNA junction of the gap using the 31-kDa domain. This
binding induces an allosteric transition, resulting in the association
of the 8-kDa domain with the dsDNA, leading to an amplification of the affinity for the gap. The 5' terminal phosphate, downstream from the
primer, has little effect on the affinity, but affects the ssDNA
conformation of the gap.
*
This work was supported by National Institutes of Health
Grant GM-58565 (to W. B).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: Dept. of Human
Biological Chemistry and Genetics, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1053. Tel.: 409-772-5643; Fax: 409-772-1790; E-mail: wbujalow@utmb.edu.
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