What proteins coordinate mismatch repair in bacteria and what is the outcome of this repair?

What proteins coordinate mismatch repair in bacteria and what is the outcome of this repair?

• A. MutS recognizes mispairs, MutL mediates, MutH nicking; exonucleases remove error; polymerase fills in.
• B. RecA and LexA coordinate mismatch repair.
• C. DNA polymerase III alone fixes mispairs.
• D. UvrABC repair complex handles mismatches.

Answer: (A)

Mismatched bases in bacteria are fixed by a methyl-directed mismatch repair system led by MutS, MutL, and MutH. MutS recognizes the wrongly paired bases, MutL acts as a coordinator, and MutH makes a nick in the newly synthesized strand near a nearby GATC site. That nick lets exonucleases remove the error-containing DNA segment from the nick back to before the mismatch. Then DNA polymerase fills in the gap using the correct template strand, and DNA ligase seals the final nick. The result is restoration of the proper base pairing and maintenance of genomic accuracy. The other proteins listed don’t fit this repair pathway: RecA and LexA regulate the SOS response rather than fixing mispairs; DNA polymerase III alone can’t correct the mispair without the nicking and excision steps; and UvrABC handles other types of DNA damage via nucleotide excision repair, not base-pair mismatches.

Mismatched bases in bacteria are fixed by a methyl-directed mismatch repair system led by MutS, MutL, and MutH. MutS recognizes the wrongly paired bases, MutL acts as a coordinator, and MutH makes a nick in the newly synthesized strand near a nearby GATC site. That nick lets exonucleases remove the error-containing DNA segment from the nick back to before the mismatch. Then DNA polymerase fills in the gap using the correct template strand, and DNA ligase seals the final nick. The result is restoration of the proper base pairing and maintenance of genomic accuracy.

The other proteins listed don’t fit this repair pathway: RecA and LexA regulate the SOS response rather than fixing mispairs; DNA polymerase III alone can’t correct the mispair without the nicking and excision steps; and UvrABC handles other types of DNA damage via nucleotide excision repair, not base-pair mismatches.