Fine structure mapping and complementation studies of themetDmethionine transport system inSalmonella typhimurium

Abstract

SummaryA fine structure deletion map of themetDregion of the chromosome ofSalmonella typhimuriumresponsible for a high-affinity methionine transport system has been constructed. Complementation tests involving the introduction ofmetD+DNA contained in a pUC8 vector intometDstrains indicated the presence of four complementation groups in themetDregion. This suggested that the methionine system belongs to the osmotic shock-sensitive class of transport system, and therefore should possess a periplasmic methionine-binding protein and several membrane proteins. But a deletion mutation covering all knownmetDpoint mutations did not affect the level of a methionine binding activity in osmotic shock fluids, suggesting either that the deletion did not extend into the gene encoding the binding protein, or that the binding activity is not associated with themetDsystem. Possible reasons for the failure to isolate mutations in the gene for the binding protein are discussed.