Ultraviolet photobiology: its early roots and insights into DNA repair.

This is the first of a series of commentaries on classic papers on DNA repair that highlight the birth of this discipline. The roots go deep, and in this first commentary, I describe some of the earliest discoveries of the mechanism of absorption of UV light in cells, and its lethal and mutagenic effects. Most remarkably, a discovery of DNA repair by the use of split doses of UV light was reported in 1919. Later commentaries will take us sequentially through the early years of DNA repair.