Psoralens as Probes of Nucleic Acid Structure and Function
This chapter discusses the psoralens in the elucidation of both DNA and RNA structure and function. The basis for many experiments in which psoralen is used as a probe for chromatin structure is the ability of the reagent to penetrate cells or isolated nuclei, bind to accessible DNA, and upon irradiation form covalent cross-links. The great advantage of these reagents is that the nucleic acid-protein cross-link can be easily reversed by reduction of the disulfide bond. The psoralens were originally characterized as a class of naturally occurring compounds and later were recognized as the pharmacological agents in folk medicines that alleviated the symptoms of vitiligo and psoriasis through photochemical action. Since the previous studies demonstrated that DNA in nucleosomes in bulk chromatin is preferentially protected from psoralen photoaddition, psoralen derivatives can be used to determine if the normal nucleosomal repeat pattern is always present.