Question

In E. coli: How does the replisome handle lesions in the template (thymidine dimers or nicks) that block DNA polymerase?

A replication fork stalls when it arrives at damaged DNA.
After the damage has been repaired, the primosome is required to reinitiate replication.

Answer 1

In E. coli, the replisome handles lesions in the template DNA that block DNA polymerase by stalling the replication fork. After the damage is repaired, the primosome is needed to restart replication. The repair process involves exonuclease trimming, RecA protein binding and filament formation, invasion of homologous DNA, and re-establishment of replication forks.

Step-by-step explanation:

In E. coli, when the replisome encounters lesions in the template DNA that block DNA polymerase, such as thymidine dimers or nicks, the replication fork stalls. After the damage has been repaired, the primosome is required to reinitiate replication. The repair process involves several steps:

1. A 5'-3' exonuclease trims the damaged DNA.
2. RecA protein monomers bind to the single-stranded DNA to form a nucleoprotein filament.
3. The RecA-DNA filament searches for homologous sequences on the opposite double-stranded DNA.
4. The filament invades the homologous DNA, separating the template and newly replicated DNA.
5. Replication of the leading strand continues from the invading strand, followed by re-establishing a new replication fork and resuming lagging strand replication.

This repair process ensures accurate repair of the original DNA damage without deletions or insertions.