The projects described in this grant proposal are aimed at elucidating some of the basic mechanisms involved in regulating the growth of cells and viruses: 1. The promotor region of a gene is that which determines the maximum intensity of gene expression of the accompanying structured regions. The promoter of a set of eight transfer RNA genes encoded for by bacteriophage T4 is being studied in vivo and in vitro. These genes have been isolated on a small DNA fragment using restriction endonucleases and their transcription by the Escherichia coli RNA polymerase is studied enzymologically as well as by nucleic acid sequencing techniques. 2. Pseudouridine is a modified base found in the so-called pseudouridine loop of animal, plant, bacterial and viral transfer RNAs. It is probable that its presence serves a regulatory function. The enzyme forming pseudouridine has now been purified (from E. coli; substrate: in vitro T4 tRNA) and is being characterized. 3. RNA synthesis in vivo and in vitro is initiated by the insertion of ATP or GTP such that the nascent RNA carries a 5'-terminal purine triphosphate. The fate and possible metabolic function of this structure is studied in E. coli. BIBLIOGRAPHIC REFERENCES: Kaplan, D. A. and Nierlich, D. P. Cleavage of non-glucosylated bacteriophage T4 DNA by restriction endonuclease Eco RI. J. Biol. Chem. 250, 2395-2397 (1975). Mowbray, S. L. and Nierlich, D. P. Regulation of RNA synthesis in Escherichia coli during a shift-up transition. Biochem. Biophys. Acta 395, 91-107 (1975).