The human cytomegalovirus UL44 C clamp wraps around DNA

Structure. 2008 Aug 6;16(8):1214-25. doi: 10.1016/j.str.2008.05.008.


Processivity factors tether the catalytic subunits of DNA polymerases to DNA so that continuous synthesis of long DNA strands is possible. The human cytomegalovirus DNA polymerase subunit UL44 forms a C clamp-shaped dimer intermediate in structure between monomeric herpes simplex virus UL42, which binds DNA directly via a basic surface, and the trimeric sliding clamp PCNA, which encircles DNA. To investigate how UL44 interacts with DNA, calculations were performed in which a 12 bp DNA oligonucleotide was docked to UL44. The calculations suggested that UL44 encircles DNA, which interacts with basic residues both within the cavity of the C clamp and in flexible loops of UL44 that complete the "circle." The results of mutational and crosslinking studies were consistent with this model. Thus, UL44 is a "hybrid" of UL42 and PCNA: its structure is intermediate between the two and its mode of interaction with DNA has elements of both.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytomegalovirus / enzymology*
  • DNA / chemistry*
  • DNA-Binding Proteins / chemistry*
  • DNA-Directed DNA Polymerase / chemistry*
  • Humans
  • Hydrogen Bonding
  • Macromolecular Substances / chemistry
  • Models, Molecular
  • Molecular Structure
  • Protein Structure, Quaternary*
  • Protein Structure, Tertiary*
  • Static Electricity
  • Viral Proteins / chemistry*


  • DNA-Binding Proteins
  • ICP36 protein, Cytomegalovirus
  • Macromolecular Substances
  • Viral Proteins
  • DNA
  • DNA-Directed DNA Polymerase