Correction rate of the first mismatch position. Correction rate of the first mismatch position after transfection with TA-clamp modified oligonucleotides carrying one mismatch (striped column) or two mismatches (black columns). The first exchange nucleotide was at hprt position 151 and the second mismatch at various distances. The X-axis indicates the distance of the second mismatch from the first exchange position in upstream and downstream direction. The Y-axis shows the mean number of clones obtained per 106 transfected cells. Mean and standard deviations were calculated based on the total number of clones after 3 – 6 transfection experiments per oligonucleotide (Additional file 1).