A series of experiments with the Lambda polA transducing phage are planned. These experiments include: Isolation of derivative phages containing partial deletions in the polA cistron. Preparation of lambda polA derivatives carrying the well characterized pola- alleles previously isolated in E. coli. Use of these phages to construct a genetic fine structure map of the polA cistron. Use of these phages to prepare mutant protein for enzymatic studies and protein chemical characterization.