Accessory proteins function as matchmakers in the assembly of the T4 DNA polymerase holoenzyme

Curr Biol. 1995 Feb 1;5(2):149-57. doi: 10.1016/s0960-9822(95)00036-4.


Background: During bacteriophage T4 DNA replication, the 44/62 and 45 accessory proteins combine with the DNA polymerase to form a processive holoenzyme complex. Formation of this complex is dependent upon ATP hydrolysis by the 44/62 protein. It is uncertain, however, whether the 44/62 protein remains with the 45 protein as part of this protein 'sliding clamp' during DNA synthesis, or whether it is required only for complex assembly.

Results: To address this tissue, we have stoichiometrically assembled a processive T4 DNA polymerase holoenzyme complex, capable of strand-displacement synthesis, on a forked primer/template. By titrating the 44/62 protein to substoichiometric concentrations, we have shown that it can act catalytically to load on to the primer/template the 45 protein, which, in turn, combines with the DNA polymerase to form a processive complex. Two distinct complex species are formed: most of the complexes are highly stable, with a half life of 7 minutes, whereas the remainder have a half-life of 0.4 minutes. Precipitation of the protein-DNA complexes, followed by western blot analysis, verified that the complexes contain the DNA polymerase and 45 proteins, but not the 44/62 protein.

Conclusion: Using physiological protein concentrations, we have shown that the composition of the T4 protein sliding clamp consists solely of the 45 protein. The role of the 44/62 protein is that of a molecular matchmaker, in that it serves to load the 45 protein onto the DNA but does not remain an essential component of the processive complex.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacteriophage T4 / enzymology*
  • Bacteriophage T4 / genetics
  • Base Sequence
  • DNA Primers
  • DNA Replication
  • DNA, Viral / biosynthesis
  • DNA, Viral / metabolism*
  • DNA-Directed DNA Polymerase / metabolism*
  • Molecular Sequence Data
  • Templates, Genetic
  • Trans-Activators / metabolism
  • Viral Proteins / metabolism*


  • DNA Primers
  • DNA, Viral
  • Trans-Activators
  • Viral Proteins
  • gene 43 protein, Enterobacteria phage T4
  • gene 44 protein, Enterobacteria phage T4
  • gene 45 protein, Enterobacteria phage T4
  • gp62 protein, bacteriophage T4
  • DNA-Directed DNA Polymerase