Abstract
Background: DNA polymerase lambda (Pol λ) was recently identified as a new member of the family X of DNA polymerases in eukaryotic cells. Pol λ contains a nuclear localization signal (NLS), a BRCA1‐C terminal (BRCT) domain, a proline‐rich region, helix‐hairpin‐helix (HhH) and pol X motifs. Since the amino acid sequence for Pol λ shares a high degree of homology to Pol β, Pol λ is considered to have a similar enzymatic nature to Pol β.
Results: Recombinant human Pol λ was shown to possess template‐directed DNA polymerase activity in its monomeric form. Pol λ required either Mn^2+^ or Mg^2+^ as a metal co‐factor to catalyse this activity, and optimal activity was detected at pH 8.5–9.0. Pol λ was insensitive to aphidicolin, but was sensitive to dideoxynucleoside triphosphates or N‐ethylmaleimide. By constructing the truncated Pol λ, the proline rich region was shown to act in a suppression of its polymerization activity. A chimeric enzyme comprised of the Pol λ N‐terminal region and Pol β also showed a reduced Pol β activity. Proliferating cell nuclear antigen (PCNA) directly interacts with Pol λ through its Pol β like region in vitro.
Conclusions: Pol λ possesses similar enzymatic nature to Pol β; requirements of cations and optimal conditions for pH and NaCl concentration, aside from sensitivity to N‐ethylmaleimide and template preference. The proline rich region of Pol λ functions as a suppressor domain for its polymerization activity (SDPA). Pol λ interacts directly with PCNA through its Pol β like region. The functional consequence of this interaction is the negative regulation of Pol λ activity.