DSSR-PyMOL cartoon-block schematics: PDB entry 6n7i

PDB-id

6n7i; DSSR-derived features in text and JSON formats

Class

hydrolase,transferase-DNA

Method

cryo-EM (3.2 Å)

Summary

Structure of bacteriophage t7 e343q mutant gp4 helicase-primase in complex with ssDNA, dttp, ac dinucleotide and ctp (gp4(5)-DNA)

Reference

Gao Y, Cui Y, Fox T, Lin S, Wang H, de Val N, Zhou ZH, Yang W (2019): "Structures and operating principles of the replisome." Science, 363. doi: 10.1126/science.aav7003.

Abstract

Visualization in atomic detail of the replisome that performs concerted leading- and lagging-DNA strand synthesis at a replication fork has not been reported. Using bacteriophage T7 as a model system, we determined cryo-electron microscopy structures up to 3.2-angstroms resolution of helicase translocating along DNA and of helicase-polymerase-primase complexes engaging in synthesis of both DNA strands. Each domain of the spiral-shaped hexameric helicase translocates sequentially hand-over-hand along a single-stranded DNA coil, akin to the way AAA+ ATPases (adenosine triphosphatases) unfold peptides. Two lagging-strand polymerases are attached to the primase, ready for Okazaki fragment synthesis in tandem. A β hairpin from the leading-strand polymerase separates two parental DNA strands into a T-shaped fork, thus enabling the closely coupled helicase to advance perpendicular to the downstream DNA duplex. These structures reveal the molecular organization and operating principles of a replisome.