A recombination-dependent replicating instability in Salmonella typhimurium.

The aromatic amino acid-requiring mutant of Salmonella typhimurium aroD321 has a stable requirement for phenylalanine and tyrosine but is highly unstable in its requirement for tryptophan. Tryptophan requiring cells derived from this strain are themselves unstable and revert back to a requirement for only phenylalanine and tyrosine. This instability is cotransducible with the aroD region and is totally dependent on the presence of a rec+ gene in the cell. These observations are interpreted in terms of a gene duplicating and excising mechanism which is itself dependent upon the normal (rec+) recombinational ability of the cell.