The long term goals are to understand how viruses interact with chromosomes and how genes for biosynthesis of proteins needed in small amounts are regulated. The health relatedness of these studies on prokaryotic model systems lies in the elucidation of basic mechanisms and in the perspective shed on natural biology of disease-causing viruses by the common features of bacterial and animal virology. The DNA of bacteriophage lambda upstream of the integrase operon will be examined for effects on integration and excision of two elements: a terminator-like sequence tI' that abuts the pI promoter and an open reading frame (ORF-55) upstream from it. Phage constructed to eliminate tI' will be examined for the effect of cII protein in the presence of transcription from pL, to test the hypothesis that tI' functions in the initial transition from the uncommitted to the lysogenic state. The ORF-55 gene expressed from a plasmid will be tested for complementation of the excisionase defect of the lambda crg phage, which has an IS2 insertion in ORF-55. Lambda crg prophages in inverted orientation will be tested for the ability to generate duplications by recombination with the defective gsr' prophage, and the defective prophages of E. coli strains of the ECOR collection will be compared. The properties of purified E. coli biotin sulfoxide reductase and the molecular basis for a newly evolved BDS reductase activity will be determined.