He identified one of the nucleases and characterized the interplay between repair factors at the site of the lesion. As a postdoc, he joined the group of Prof. Frank Grosveld to work on beta-globin gene activation. In 2000 he received a career grant (VIDI) to work on long-range gene activation. His group used 3C technology, and later developed 4C technology, to demonstrate chromatin loops between genes and enhancers and to uncover long-range DNA contacts within and between chromosomes.