EMD-0359
Structure of bacteriophage T7 E343Q mutant gp4 helicase-primase in complex with ssDNA, dTTP, AC dinucleotide and CTP (form I)
EMD-0359
Single-particle3.5 Å
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Map released: 06/03/2019
Last modified: 20/03/2024
Sample Organism:
Enterobacteria phage T7
Sample: Bacteriophage T7 gene product 4 (gp4) helicase primase DNA complex I
Fitted models: 6n7n (Avg. Q-score: 0.421)
Deposition Authors: Gao Y
,
Cui Y
Sample: Bacteriophage T7 gene product 4 (gp4) helicase primase DNA complex I
Fitted models: 6n7n (Avg. Q-score: 0.421)
Deposition Authors: Gao Y
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Structures and operating principles of the replisome.
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.
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.