title: Variations with position of replication errors due to exonuclease warm-up.
abstract: A.A mismatch errors occurring during poly(dA) replication with the Klenow fragment of E. coli DNA polymerase I have been quantified. The A/T ratio measured for chains extended by 1-25 nucleotides decreases by a factor of at least 15 from beginning to end. The deduced true error rate may decrease by a factor of 2.5 at each successive nucleotide addition. When ddATP is used instead of dATP, the ddA/T ratio indicates little variation of the misincorporation probability with position. Thus, the accuracy improvement in the first case is due to a warm-up of the proofreading function.
mesh_terms: D001482:Base Composition; D004261:DNA Replication; D005092:Exonucleases / Q000494:pharmacology*; D011061:Poly A / Q000378:metabolism
chemical_list: D011061:Poly A; C015465:poly(dA); D005092:Exonucleases