Final answer:
While a DNA polymerase can detect and rectify mismatches through its proofreading function, once it moves on, the incorrect tautomeric base pairing may escape immediate detection and may require mismatch repair mechanisms to correct.
Step-by-step explanation:
Is it possible for a replicative DNA polymerase to cleave a base paired tautomer if it has left the polymerase? In the context of DNA replication, the DNA polymerase has an intrinsic proofreading function that checks the fidelity of base-pairing immediately after the incorporation of a nucleotide. This proofreading activity involves the polymerase detecting any mismatches, including those arising from tautomeric shifts, and excising the incorrect base via its 3' to 5' exonuclease activity.
Essentially, if a base pair is incorrect due to a tautomeric shift that causes an improper hydrogen bonding arrangement, DNA polymerase can identify this before adding the next nucleotide. However, once the polymerase has moved on and the mismatched base is no longer within the polymerase’s proofreading domain, the mistake becomes part of the DNA and may require mismatch repair systems to resolve.
Furthermore, the mismatch repair mechanism comes into play after replication to correct errors that elude the proofreading activity of DNA polymerase. This repair system detects and excises the incorrect base, then fills in the gap with the correct base, preventing potential permanent damage to the DNA.