5iud
From Proteopedia
Human DNA polymerase alpha in binary complex with a DNA:DNA template-primer
Structural highlights
Function[DPOLA_HUMAN] Plays an essential role in the initiation of DNA replication. During the S phase of the cell cycle, the DNA polymerase alpha complex (composed of a catalytic subunit POLA1/p180, a regulatory subunit POLA2/p70 and two primase subunits PRIM1/p49 and PRIM2/p58) is recruited to DNA at the replicative forks via direct interactions with MCM10 and WDHD1. The primase subunit of the polymerase alpha complex initiates DNA synthesis by oligomerising short RNA primers on both leading and lagging strands. These primers are initially extended by the polymerase alpha catalytic subunit and subsequently transferred to polymerase delta and polymerase epsilon for processive synthesis on the lagging and leading strand, respectively. The reason this transfer occurs is because the polymerase alpha has limited processivity and lacks intrinsic 3' exonuclease activity for proofreading error, and therefore is not well suited for replicating long complexes.[1] Publication Abstract from PubMedThe Polalpha/primase complex assembles the short RNA-DNA fragments for priming of lagging and leading strand DNA replication in eukaryotes. As such, the Polalpha polymerase subunit encounters two types of substrates during primer synthesis: an RNA:DNA helix and a DNA:DNA helix. The engagement of the polymerase subunit with the DNA:DNA helix has been suggested as the of basis for primer termination in eukaryotes. However, there is no structural information on how the Polalpha polymerase subunit actually engages with a DNA:DNA helix during primer synthesis. We present here the first crystal structure of human Polalpha polymerase subunit in complex with a DNA:DNA helix. Unexpectedly, we find that portion of the DNA:DNA helix in contact with the polymerase is not in a B-form but in a hybrid A-B form. Almost all of the contacts observed previously with an RNA primer are preserved with a DNA primer - with the same set of polymerase residues tracking the sugar-phosphate backbone of the DNA or RNA primer. Thus, rather than loss of specific contacts, the free energy cost of distorting DNA from B- to hybrid A-B form may augur the termination of primer synthesis in eukaryotes. Human DNA polymerase alpha in binary complex with a DNA:DNA template-primer.,Coloma J, Johnson RE, Prakash L, Prakash S, Aggarwal AK Sci Rep. 2016 Apr 1;6:23784. doi: 10.1038/srep23784. PMID:27032819[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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