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Molecular and Cellular Biology, February 2005, p. 1183-1190, Vol. 25, No. 3
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.3.1183-1190.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

A Single Domain in Human DNA Polymerase {iota} Mediates Interaction with PCNA: Implications for Translesion DNA Synthesis

Lajos Haracska,1,2 Narottam Acharya,2 Ildiko Unk,1,2 Robert E. Johnson,2 Jerard Hurwitz,3 Louise Prakash,2 and Satya Prakash2*

Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary,1 Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston, Texas,2 Department of Molecular Biology and Virology, Memorial Sloan-Kettering Cancer Center, New York, New York3

Received 12 October 2004/ Returned for modification 28 October 2004/ Accepted 31 October 2004

DNA polymerases (Pols) of the Y family rescue stalled replication forks by promoting replication through DNA lesions. Humans have four Y family Pols, {eta}, {iota}, {kappa}, and Rev1, of which Pols {eta}, {iota}, and {kappa} have been shown to physically interact with proliferating cell nuclear antigen (PCNA) and be functionally stimulated by it. However, in sharp contrast to the large increase in processivity that PCNA binding imparts to the replicative Pol, Pol{delta}, the processivity of Y family Pols is not enhanced upon PCNA binding. Instead, PCNA binding improves the efficiency of nucleotide incorporation via a reduction in the apparent Km for the nucleotide. Here we show that Pol{iota} interacts with PCNA via only one of its conserved PCNA binding motifs, regardless of whether PCNA is bound to DNA or not. The mode of PCNA binding by Pol{iota} is quite unlike that in Pol{delta}, where multisite interactions with PCNA provide for a very tight binding of the replicating Pol with PCNA. We discuss the implications of these observations for the accuracy of DNA synthesis during translesion synthesis and for the process of Pol exchange at the lesion site.

* Corresponding author. Mailing address: Sealy Center for Molecular Science, University of Texas Medical Branch, 6.104 Medical Research Building, 11th and Mechanic Streets, Galveston, TX 77555-1061. Phone: (409) 747-8602. Fax: (409) 747-8608. E-mail: s.prakash{at}utmb.edu.

Molecular and Cellular Biology, February 2005, p. 1183-1190, Vol. 25, No. 3
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.3.1183-1190.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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