| Replication protein A | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (heterotrimer) | |||||||||||||
 This is an image of human Replication protein A. FromPDB:1L1OProteopediaprotein A Replication protein A | |||||||||||||
| Function | damaged DNA binding, single-stranded DNA binding | ||||||||||||
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Replication protein A (RPA) is the majorprotein that binds to single-strandedDNA (ssDNA) ineukaryotic cells.[1][2]In vitro, RPA shows a much higher affinity for ssDNA than RNA or double-stranded DNA.[3] RPA is required inreplication,recombination and repair processes such asnucleotide excision repair andhomologous recombination.[2][4] It also plays roles in responding to damaged DNA.[4]
RPA is aheterotrimer, composed of the subunits RPA1 (RPA70) (70kDa subunit), RPA2 (RPA32) (32kDa subunit) and RPA3 (RPA14) (14kDa subunit). The three RPA subunits contain sixOB-folds (oligonucleotide/oligosaccharide binding), withDNA-binding domains (DBD) designated DBDs A-F, that bind RPA tosingle-stranded DNA.[2][3]
DBDs A, B, C and F are located on RPA1, DBD D is located on RPA2, and DBD E is located on RPA3.[4] DBDs C, D, and E make up the trimerization core of the protein withflexible linker regions connecting them all together.[4] Due to these flexible linker regions RPA is considered highly flexible and this supports the dynamic binding that RPA is able to achieve. Because of this dynamic binding, RPA is also capable of different conformations that leads to varied numbers of nucleotides that it can engage.[4]
DBDs A, B, C and D are the sites that are involved in ssDNA binding.[5] Protein-protein interactions between RPA and other proteins happen at theN-terminal of RPA1, specifically DBD F, along with theC-terminal of RPA2.[5]Phosphorylation of RPA takes place at the N-terminus of RPA2.[5]
RPA shares many features with theCST complex heterotrimer, although RPA has a more uniform 1:1:1stoichiometry.[6]
During DNA replication, RPA prevents single-stranded DNA (ssDNA) from winding back on itself or from forming secondary structures. It also helps protect the ssDNA from being attacked byendonucleases.[2] This keeps DNA unwound for thepolymerase to replicate it. RPA also binds to ssDNA during the initial phase of homologous recombination, an important process inDNA repair andprophase I ofmeiosis.
RPA has a key role in the maintenance of therecombination checkpoint duringmeiosis of the yeastSaccharomyces cerevisiae.[7] RPA appears to act as a sensor of single-strand DNA for the activation of the meiotic DNA damage response.[7]
Hypersensitivity to DNA damaging agents can be caused bymutations in the RPA gene.[8] Like its role in DNA replication, this keeps ssDNA from binding to itself (self-complementizing) so that the resultingnucleoprotein filament can then be bound byRad51 and its cofactors.[8]
RPA also binds to DNA during the nucleotide excision repair process. This binding stabilizes the repair complex during the repair process. A bacterial homolog is calledsingle-strand binding protein (SSB).
| Excision repair | |
|---|---|
| Homologous recombination | |
| Other pathways | |
| Regulation | |
| Other/ungrouped | |
