New methods for probing nucleic acids

Modern molecular biology depends on the ability to manipulate DNA. Cloning and other genetic engineering techniques require the specific cleavage of DNA at restriction sites (see below). One method of sequencing nucleic acids relies on base-specific chemical reactions, and several structure-specific ribonucleases are used to probe the secondary and tertiary structure of RNA. There is a great deal of interest in new techniques for studying the structure and function of DNA and RNA. Also, the advent of pulsed field gradient electrophoresis' has made it possible to analyze chromosome-size DNA, and this suggests the extension of probing techniques to this realm. (The size of a typical plasmid is N 5 kb, h phage is 40 kb, the E. coli chromosome is 5 Mb, and the human X-chromosome is 50 Mb; common techniques are useful up to a size of perhaps 50 kb.) We will briefly review some advances in enzymatic and chemical mapping and discuss possibilities for studying structure in nucleic acids and for restricting large DNA's.