Consider a colony of E. coli that might develop from a single founder cell on a

Question

Consider a colony of E. coli that might develop from a single founder cell on a petri dish. Looking at just the methyl-directed mismatch repair system in prokaryotes, explain what the effect would be if the founder carried a mutation that caused the mechanism for methylating new strands of nucleotides to become 1000-fold faster. Use specific references to the methyl-directed mismatch repair system (Figure 7.17 of text) to support what you think the effect would be and be detailed in explaining the sequence of consequences that would follow as it affects the developing colony.

Explanation / Answer

DNA mismatch repair is a system that has evolved to identify wrongly inserted bases while replication. The three proteins which play a very important role are MutS, MutH and MutL. MutS forms a dimer (MutS2) that recognises the mismatched base on the daughter strand and binds the mutated DNA. MutH binds at hemimethylated sites along the daughter DNA, but its action is latent, being activated only upon contact by a MutL dimer (MutL2), which binds the MutS-DNA complex and acts as a mediator between MutS2 and MutH, activating the latter. Hence mutation in any of these genes would lead to an exclusion of the check that these proteins usually carry out. In absence of an inspection the ability to recognise a mutation or hemimethylate the newly synthesized strand would be lost and the DNA would be constitutively methylated. In short, the whole colony would be full of mutations with severe impairment in the phenotype due to severely mutated genotype.

"A malaria biologist"

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.