Question

What happens during the RecA-mediated postsynapsis stage in strand exchange?

a RecA recruits SSB to loosen DNA hairpins.
b RecA and SSB act together to coat ss DNA.
c Ss DNA 3-protruding strand starts to penetrate ds DNA.
d Ss DNA replaces one strand in the ds DNA resulting in two DNAs intertwined in a joint molecule intermediate.

Answer 1

The RecA-mediated postsynapsis stage involves a 3'-protruding ssDNA strand, coated by RecA, invading a homologous dsDNA and exchanging strands to form a joint molecule intermediate with intertwined DNAs.

Step-by-step explanation:

During the RecA-mediated postsynapsis stage in strand exchange, the single-stranded DNA (ssDNA) that is coated with RecA nucleoprotein filament undergoes a process called strand invasion. This process involves the 3'-protruding ssDNA strand penetrating the double-stranded DNA (dsDNA). Once the homologous sequences are located, strand exchange occurs where the ssDNA replaces one strand of the dsDNA, leading to the formation of a joint molecule intermediate that includes two DNAs intertwined. This is the precursor to the formation of crossover products that can be resolved to complete the repair process.

It is important to note that the RecA protein facilitates the search for homology and the pairing between the ssDNA and complementary strands in the dsDNA. The outcome is a new synthesis of DNA that accurately repairs the initial damage without deletions or insertions.