E.Coli DNa Pol III consists of a 5'3' polymerase activity and a 3'5' proofreading activity. lets...

E.Coli DNa Pol III consists of a 5'3' polymerase activity and a 3'5' proofreading activity. lets assume that a novel mutation results in a defective DNA Pol III, which can normally Polymerize nucleotides But can't proofread accurately. This error prone polymerase may result in one mistake per 100 base pairs. In order to prevent extensive damage to the genome, the micro must recruit a DNA repair mechanism. The microbe should be able to identify the newly synthesized strand of DNA and make the needed repairs. Using your knowledge of the DNA repair mechanisms answer the following questions.

a. which repair mechanism would be most suitable for this type of fixing?

b. how does the repair system recognize the parental strand with the correct code?

c. Which enzymes will help make the correction? Explain the process

Expert Solution

1. DNA Mismatch repair is most suitable that recognize and repair mis-incorporation of bases during DNA replication and recombination.

2. The newly synthesized (daughter) strand usually contains errors during the DNA synthesis. The mismatch repair system differentiates the newly synthesized strand from the parental strand to begin repair since it is strand specific. The repair mechanism recognize the parental strand with the help of transient hemimethylation as the parental strand is methylated by the action of DNA methyltransferases while the newly synthesized DNA strand is not.

3. Enzymes that help to make correction are endonucleas, ligases, polymerases and SSB and the proteins associated with it are MutS, MutH, MutL and PCNA β-sliding clamp.

The process is as follows:

The pecific proteins scans the newly synthesized DNA strand by adenine methylation at GATC.
MutS homolog protein recognize and binds to the mismatch.
MutS recruit MutL to the mismatch side and binds to it increasing MutS footprint on the DNA.
Both activate MutH, an endonuclease, which binds to MutL and nicks the unmethylated DNA strand carrying mismatch.
With the aid of PCNA, DNA polymerase adds new nucleotides to fill the gap.
The gap/nick is then sealed by DNA ligase.

gladiator answered 3 hours ago

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