Structural and functional analysis of cloned DNA containing genes responsible for branched-chain amino acid transport in Escherichia coli.

The four genes encoding the components of the high-affinity branched-chain amino acid transport systems in Escherichia coli (livH, livG, livJ, and livK) have been cloned into lambda phage and subsequently into the plasmid vector pACYC184. The presence of the four structural genes and their accompanying regulatory regions on the resultant plasmid, pOXI, was confirmed by genetic complementation and analysis and by transport studies carried out on the appropriate transformed mutant strains. When pOX1 DNA was used to direct an in vitro transcription/translation system, four major polypeptide products were produced. Immunoprecipitation with antibody directed against the LIV-binding protein identified the two leucine-binding proteins as products of in vitro synthesis. The binding proteins were produced in precursor forms and had molecular weights approximately 2500 higher than the processed, mature forms. A minicell-producing strain transformed with plasmid pOX1 produced the binding proteins in the processed form.