Question

What would the effect be if each of the different sub-units of E.coli DNA polymerases were not functioning?

Answer 1

E. coli contains 5 different DNA polymerases: DNA Pol I, DNA Pol II, DNA Pol III, DNA Pol IV, and DNA Pol V.

The physiological function of Pol I is mainly to repair any damage with DNA, but it also serves to connect Okazaki fragments by deleting RNA primers and replacing the strand with DNA. Pol I, encoded by polA, plays roles in processing Okazaki fragments and also in gap-filling during excision-repair processes.

Pol II is encoded by polB. It is an accurate DNA polymerase because, like Pol I, it has an editing or proofreading 3′-exonuclease domain that can erode a mispaired primer end and so remove incorrectly inserted bases. It participates in some repair processes

Pol III has its editing function provided by the dnaQ encoded epsilon subunit of the Pol III holoenzyme The main replicative polymerase is Pol III. The catalytic subunit, designated Pol III, is encoded by dnaE

Pol IV or DinB, is required for stress-induced mutagenesis Pol IV is recruited to acts of DNA double-strand-break repair, and causes mutagenesis, only when at least two cellular stress responses are activated

Pol V functions as a TLS(translesion DNA synthesis) 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. 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.

If each of the different sub-units of E.coli DNA polymerases were not functioning,there will be many modifications in the DNA replication process.

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