The difficulty in this system is identifying which strand contains the incorrect nucleotide. This is done in prokaryotes by taking advantage of the fact that when a DNA sequence 5 GATC3 occurs, the adenine will be methylated in prokaryotes. However, this methylation occurs post-replication. Therefore, there is a short period of time during which only one of the two DNA strands is methylated and this represents the older strand and the one with the correct sequence. The methylation site does not have to exist extremely near the mismatch.
Recombinational repair is a process that occurs post replication.
When a strand containing a major DNA lesion is to be replicated the complement is synthesized in such a way that a gap is left opposite the region containing the lesion. The details concerning how this is done by DNA polymerase have yet to be worked out. After replication, a region of the other DNA strand in the original DNA molecule is used to fill in the missing gap. Now the other original strand is missing a gap. This gap is synthesized by using its newly synthesized complement as a template.