The overall objective of the work is to advance the knowledge of the hydrodynamic and some other structural parameters which determine the behavior of single-stranded DNA and various forms of duplex DNA. Kinetic and equilibrium ultracentrifugation techniques and gel electrophoresis methods will be the major techniques employed. Specific projects either completed or to be carried out include: 1) measurement of the Kuhn statistical length and excluded volume parameter for single-stranded DNA at neutral pH under conditions where the hydrodynamic behavior of the DNA is amenable to treatment with an existing theory; 2) measurement of the excluded volume parameter for duplex DNA through a new method developed in connection with this research; 3) studies as to the nature of the finite number of unique sites in supercoiled PM2 phage closed circular DNA which preliminary work has shown are attacked by a highly non-duplex structure-specific nuclease isolated in this laboratory, and studies to ascertain whether these sites can be identified with sites of initiation of transcription; 4) further studies as to the nature of the process leading to irreversible denaturation in closed circular PM2 DNA, which appears to be distinct form the behavior of other closed circular DNAs in this regard (this work largely completed); 5) studies on an interesting phenomenon in which intercalating dyes, present in very strongly alkaline solutions of closed circular DNA, can lead to the renaturation of such DNA (work completed).