Pol V
| DNA polymerase V, subunit C | |
|---|---|
| Identifiers | |
| Organism |
(str. K-12 substr. MG1655) |
| Symbol | umuC |
| Entrez | 946359 |
| RefSeq (Prot) | NP_415702.1 |
| UniProt | P04152 |
| Other data | |
| EC number | 2.7.7.7 |
| Chromosome | genome: 1.23 - 1.23 Mb |
| DNA polymerase V, subunit D | |
|---|---|
| Identifiers | |
| Organism |
(str. K-12 substr. MG1655) |
| Symbol | umuD |
| Entrez | 945746 |
| RefSeq (Prot) | NP_415701.1 |
| UniProt | P0AG11 |
| Other data | |
| EC number | 3.4.21.- |
| Chromosome | genome: 1.23 - 1.23 Mb |
DNA Polymerase V (Pol V) is a polymerase enzyme involved in DNA repair mechanisms in prokaryotic bacteria, such as Escherichia coli. It is composed of a UmuD' homodimer and a UmuC monomer, forming the UmuD'2C protein complex. It is part of the Y-family of DNA Polymerases, which are capable of performing DNA translesion synthesis (TLS). Translesion polymerases bypass DNA damage lesions during DNA replication - if a lesion is not repaired or bypassed the replication fork can stall and lead to cell death. However, Y polymerases have low sequence fidelity during replication (prone to add wrong nucleotides). When the UmuC and UmuD' proteins were initially discovered in E. coli, they were thought to be agents that inhibit faithful DNA replication and caused DNA synthesis to have high mutation rates after exposure to UV-light. The polymerase function of Pol V was not discovered until the late 1990s when UmuC was successfully extracted, consequent experiments unequivocally proved UmuD'2C is a polymerase. This finding lead to the detection of many Pol V orthologs and the discovery of the Y-family of polymerases.
Pol V functions as a TLS polymerase in E. coli as part of the SOS response to DNA damage. When DNA is damaged regular DNA synthesis polymerases are unable to add dNTPs onto the newly synthesized strand. DNA Polymerase III (Pol III) is the regular DNA polymerase in E. coli. As Pol III stalls unable to add nucleotides to the nascent DNA strand, the cell becomes at risk of having the replication fork collapse and apoptosis to take place. Pol V TLS function depends on association with other elements of the SOS response, most importantly Pol V translesion activity is tightly dependent on the formation of RecA nucleoprotein filaments. Pol V can use TLS on lesions that block replication or miscoding lesions, which modify bases and lead to wrong base pairing. However, it is unable to translate through 5' → 3' backbone nick errors. Pol V also lacks exonuclease activity, thus rendering unable to proofread synthesis causing it to be error prone.
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