UV Laser-Induced Protein-DNA Crosslinking

Photochemical crosslinking is a powerful method for studying all types of protein-nucleic acids interactions. In particular, UV-induced crosslinking has been successfully applied to the study of protein-DNA interactions (1 ). Ultraviolet (UV) light is a zero-length crosslinking agent. It is therefore not subject to the steric problems that can be associated with chemical crosslinking agents and provides strong evidence for close protein-DNA interactions. However, to achieve an acceptable degree of crosslinking with conventional UV light sources, exposure times ranging from minutes to several hours have had to be used (1 –3 ). Such prolonged irradiation allows for redistribution of proteins and the artifactual crosslinking of UV-damaged molecules, and it also precludes kinetic studies. The use of UV lasers overcomes these difficulties, since crosslinking is achieved after only nano- or picosecond exposures (4 –5 ).