Paul Modrich – illustrating DNA mismatch repair For Paul Modrich, this discovery kick-started a decade of systematic work, cloning and mapping one enzyme after the other in the mismatch repair process. Towards the end of the 1980s, he was able to recreate the complex molecular repair mechanism in vitro and study it in great detail. This work was published in 1989. Paul Modrich, just like Tomas Lindahl and Aziz Sancar, has also studied the human version of the repair system. Today we know that all but one out of a thousand errors that occur when the human genome is copied, are corrected by mismatch repair. However, in human mismatch repair, we still do not know for sure how the original strand is identified. DNA methylation has other functions in our genome to that of bacteria, so something else must govern which strand gets corrected – and exactly what remains to be clarified.