The general aim of this project is the genetic and biochemical characterization of a number of metabolite transport systems in Escherichia coli, with emphasis on the structural relationships of the component proteins. The proposed studies for the coming year will center on the vitamin B12 uptake systems. Two components of this uptake system have been defined genetically. There is an outer membrane receptor, coded by the bfe locus, which is also involved in the cellular binding of the E colicins and bacteriophage BF23. Several functional states for this receptor with respect to colicin binding have been defined. In addition, a protein, coded by the tonB gene, is necessary for the uptake of B12 as well as iron chelates, the group B colicins and phages T1 and phi80. It is the identity, location, role and interactions of the tonB product that is the object of study in this project. Its stability is studied both inhibition of general protein synthesis and by the specific cessation of its synthesis with a temperature-sensitive suppressor system. The turnover of other membrane systems are also being studied in this way. Amplified synthesis of the tonB product will be attempted with the use of specialized transducing phages. BIBLIOGRAPHIC REFERENCES: Bassford, Jr., P.J., C. Bradbeer, R.J. Kadner, and C.A. Schnaitman. 1976. Transport of vitamin B12 in tonB mutants of Escherichia coli. J. Bacteriol. October issue. Bassford, Jr., P.J., R.J. Kadner, and C.A. Schnaitman. 1976. Biosynthesis of the outer membrane receptor for vitamin B12, E colicins, and phage BF23 by Escherichia coli: A study of the kinetcs of phenotypic expression following the introduction of Bfe+ and Bfe- alleles. J. Bacteriol., in press.