A mechanism for the control of patch size in mammalian cell DNA excision repair

The hypothesis is suggested that size of the region excised in repair of UV-induced damage in mammalian cell is determined by the occurrence at random of a recognition sequence which terminates this excision process. The statistics of first occurrence times for a specific nucleotide sequence in a random chain are derived and shown to lead to an approximately random distribution of sizes around the average. The heterogeneity in sizes arising from a model are shown not to conflict with existing measurements. A sequence of length three or four is sufficient to account for the measured average size.