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Mutant bacteriophage T4 gp41 helicase hexamer bound with single strand DNA and ATPgammaS in the stalled primosome
Structural highlights
FunctionA0A7S9SV99_BPT4 ATP-dependent DNA helicase essential for viral DNA replication and recombination. The helicase moves 5' -> 3' on the lagging strand template, unwinding the DNA duplex ahead of the leading strand polymerase at the replication fork and generating ssDNA for both leading and lagging strand synthesis. Interaction with the primase allows the primase to initiate lagging strand synthesis and fully activates the helicase. Loaded by the helicase assembly factor on replication forks that begin at discrete replication origin sequences, as well as on forks that are created during recombination.[HAMAP-Rule:MF_04155] Publication Abstract from PubMedThe T4 bacteriophage gp41 helicase and gp61 primase assemble into a primosome complex to couple DNA unwinding with RNA primer synthesis for DNA replication. How a primosome is assembled and how the length of the RNA primer is defined in the T4 bacteriophage, or in any model system, are unclear. Here we report a series of cryo-EM structures of T4 primosome assembly intermediates at resolutions up to 2.7 A. We show that the gp41 helicase is an open spiral in the absence of ssDNA, and ssDNA binding triggers a large-scale scissor-like conformational change that drives the open spiral to a closed ring that activates the helicase. We found that the activation of the gp41 helicase exposes a cryptic hydrophobic primase-binding surface allowing for the recruitment of the gp61 primase. The primase binds the gp41 helicase in a bipartite mode in which the N-terminal Zn-binding domain (ZBD) and the C-terminal RNA polymerase domain (RPD) each contain a helicase-interacting motif (HIM1 and HIM2, respectively) that bind to separate gp41 N-terminal hairpin dimers, leading to the assembly of one primase on the helicase hexamer. Based on two observed primosome conformations - one in a DNA-scanning mode and the other in a post RNA primer-synthesis mode - we suggest that the linker loop between the gp61 ZBD and RPD contributes to the T4 pentaribonucleotide primer. Our study reveals T4 primosome assembly process and sheds light on RNA primer synthesis mechanism. Structural basis of the T4 bacteriophage primosome assembly and primer synthesis.,Feng X, Spiering MM, de Luna Almeida Santos R, Benkovic SJ, Li H bioRxiv. 2023 May 3:2023.05.03.539249. doi: 10.1101/2023.05.03.539249. Preprint. PMID:37205424[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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