Practice question

Taq polymerase retains 5' to 3' polymerase activity necessary for nucleotide incorporation and 5' to 3' exonuclease activity useful for nick translation, but lacks 3' to 5' exonuclease function that mediates proofreading. This absence means polymerase cannot reverse and remove incorrectly paired bases at the growing 3' terminus, leading to fixed mutations in amplicons. The structural basis is absence of exonuclease domain. Knowledge of domain architecture explains error spectrum and rationale for blending Taq with proofreading enzymes for long PCR.