Published online 16 January 2004
Nucleic Acids Research, 2004, Vol. 32, No. 1 361-370
© 2004 Oxford University Press
Function of the C-terminus of 
29 DNA polymerase in DNA and terminal protein binding
Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain
*To whom correspondence should be addressed. Tel: +34 91 3978435; Fax: +34 91 3978490; Email: msalas{at}cbm.uam.es
Present address:
Verónica Truniger, CEBAS, Campus Universidad de Murcia, 30100 Espinardo, Murcia, Spain
The thumb subdomain, located in various family B DNA polymerases in the C-terminal region, has been shown in their crystal structures to move upon binding of DNA, changing its conformation to nearly completely wrap around the DNA. It has therefore been involved in DNA binding. In agreement with this, partial proteolysis studies of 
29 DNA polymerase have shown that the accessibility of the cleavage sites located in their C-terminal region is reduced in the presence of DNA or terminal protein (TP), indicating that a conformational change occurs in this region upon substrate binding and suggesting that this region might be involved in DNA and TP binding. Therefore, we have studied the role of the C-terminus of 29 DNA polymerase by deletion of the last 13 residues of this enzyme. This fragment includes a previously defined region conserved in family B DNA polymerases. The resulting DNA polymerase 
13 was strongly affected in DNA binding, resulting in a distributive replication activity. Additionally, the capacity of the truncated polymerase to interact with TP was strongly reduced and its initiation activity was very low. On the other hand, its nucleotide binding affinity and its fidelity were not affected. We propose that the C-terminal 13 amino acids of 29 DNA polymerase are involved in DNA binding and in a stable interaction with the initiator protein TP, playing an important role in the intrinsic processivity of this enzyme during polymerization.
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