A ring-opening mechanism for DNA binding in the central channel of the T7 helicase–primase protein
AUTOR(ES)
Ahnert, Peter
FONTE
Oxford University Press
RESUMO
We have investigated the mechanism of binding single-stranded DNA (ssDNA) into the central channel of the ring-shaped T7 gp4A′ helicase–primase hexamer. Presteady-state kinetic studies show a facilitated five-step mechanism and provide understanding of how a ring-shaped helicase can be loaded on the DNA during the initiation of replication. The effect of a primase recognition sequence on the observed kinetics suggests that binding to the helicase DNA-binding site is facilitated by transient binding to the primase DNA-binding site, which is proposed to be a loading site. The proposed model involves the fast initial binding of the DNA to the primase site on the outside of the helicase ring, a fast conformational change, a ring-opening step, migration of the DNA into the central channel of the helicase ring, and ring closure. Although an intermediate protein–DNA complex is kinetically stable, only the last species in the five-step mechanism is poised to function as a helicase at the unwinding junction.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=313936Documentos Relacionados
- Interaction of adjacent primase domains within the hexameric gene 4 helicase-primase of bacteriophage T7
- A unique loop in T7 DNA polymerase mediates the binding of helicase-primase, DNA binding protein, and processivity factor
- The DNA-unwinding mechanism of the ring helicase of bacteriophage T7
- An N-terminal fragment of the gene 4 helicase/primase of bacteriophage T7 retains primase activity in the absence of helicase activity
- Bacteriophage T7 helicase/primase proteins form rings around single-stranded DNA that suggest a general structure for hexameric helicases.