Pseudomonas aeruginosa easily acquires resistance to a wide range of antibiotics through the acquisition of extrachromosomal deoxyribonucleic acid elements, (R factor) which contains the genetic information for cellular conversion to antibiotic resistance. Understanding cellular contribution to replication and maintenance of these genetic elements within the host cell, is of prime importance in understanding total genetic potentiality of the bacterial species. The phenotype of lysogeny-establishment deficiency (Les) leads to the inability of temperate bacteriophage to establish lysogeny. Les is a mutant phenotype of the bacterium. This project will exploit this phenotype to identify genetically and biochemically the mechanisms of establishment and maintenance of new DNA elements within the cell. To date, les mutations have been isolated in several genes. Most mutations affect only the establishment of lysogeny, while specific mutations have pleiotropic effects on recombination, DNA repair, and stability of the sex factor FP2. In addition, an indirect suppressor of the Les phenotype (sly) has been identified which is associated with the sex factor FP2 plasmid cointegrate. The major aim of the research proposed is a biochemical study of the cellular components which are the products of these genes. Several enzymes which will be investigated are: (1) adenylate cyclase, (2) DNA gyrase, (3) Pseudomonas exonuclease V and (4) Pseudomonas exonuclease I. Several lines of evidence suggest the probability of a role of these enzymes in the establishment of lysogeny in the bacterial cells. Additional genetic studies are also proposed. These will center on (1) further characterization of the pleiotropic consequences of the Les phenotype (especially with respect to the establishment of plasmid elements), (2) characterization of the sly gene and an estimation of its frequency among Pseudomonas plasmids, and (3) the search for les genes which specifically affect the ability of the plasmid prophage of F116 to establish lysogeny in its host.