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Molecular and Cellular Biology, March 2001, p. 2018-2025, Vol. 21, No. 6
Sealy Center for Molecular Science,
University of Texas Medical Branch, Galveston, Texas 77555-1061
Received 28 November 2000/Returned for modification 18 December
2000/Accepted 20 December 2000
Rad30 is a member of the newly discovered UmuC/DinB/Rad30
family of DNA polymerases. The N-terminal regions of these proteins are
highly homologous, and they contain five conserved motifs, I to V,
while their C-terminal regions are quite divergent. We examined the
contributions of the C-terminal and N-terminal regions of Rad30 to its
activity and biological function. Although deletion of the last 54 amino acids has no effect on DNA polymerase or thymine-thymine (T-T)
dimer bypass activity, this C-terminal deletion-containing protein is
unable to perform its biological function in vivo. The presence of a
bipartite nuclear targeting sequence within this region
suggests that at least one function of this portion of Rad30 is nuclear
targeting. To identify the active-site residues of Rad30 important for
catalysis, we generated mutations of nine acidic residues that are
invariant or highly conserved among Rad30 proteins from different
eukaryotic species. Mutations of the Asp30 and Glu39 residues present
in motif I and of the Asp155 residue present in motif III to alanine
completely inactivated the DNA polymerase and T-T dimer bypass
activities, and these mutations did not complement the UV sensitivity
of the rad30
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.6.2018-2025.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Acidic Residues Critical for the Activity
and Biological Function of Yeast DNA Polymerase
mutation. Mutation of Glu156 in motif III
to alanine confers a large reduction in the efficiency of nucleotide
incorporation, whereas the remaining five Rad30 mutant proteins retain
wild-type levels of DNA polymerase and T-T dimer bypass activities.
From these observations, we suggest a role for the Asp30, Glu39, and
Asp155 residues in the binding of two metal ions required for the
reaction of the incoming deoxynucleoside 5'-triphosphate with the
3'-hydroxyl in the primer terminus, while Glu156 may participate in
nucleotide binding.
*
Corresponding author. Mailing address: University of
Texas Medical Branch, Sealy Center for Molecular Science, 6.104 Medical Research Building, 11th and Mechanic St., Galveston, TX 77555-1061. Phone: (409) 747-8601. Fax: (409) 747-8608. E-mail:
lprakash{at}scms.utmb.edu.
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