TRYPTOPHAN SYNTHETASE LEVELS IN ESCHERICHIA COLI, SHIGELLA DYSENTERIAE , AND TRANSDUCTION HYBRIDS

Abstract

Shigella dysenteriae and Escherichia coli, strains K-12 and B, were found to produce low levels of tryptophan synthetase, although some hybrids, formed by the introduction of the gene cluster concerned with tryptophan synthesis from S. dysenteriae into E. coli, produced high levels of this enzyme system. A revertant obtained from a tryptophan-requiring mutant also formed high levels of tryptophan synthetase. The gene or genes responsible for high enzyme production in these strains was shown to be linked to the cluster of genes concerned with tryptophan synthesis. The cause of high enzyme production was investigated. Various lines of evidence, including stimulation of growth by tryptophan precursors, sensitivity to inhibition by 5-methyltryptophan, absence of accumulation of tryptophan, and repression of enzyme formation by anthranilic acid and tryptophan, suggested that high enzyme production in the strains examined results from a partial block in the tryptophan pathway and not from resistance to repression by tryptophan. The conversion of shikimic acid-5-phosphate to anthranilic acid appears to be the partially blocked reaction in the strains studied.

Tryptophan operon regulation in interspecific hybrids of enteric bacteria

“…coli and Salmonella typhimurium (50) and ofE. coli and Shigella dysenteriae (13). Our results are consistent with and expand upon their findings.…”

“…126, 1976 on August 11, 2020 by guest http://jb.asm.org/ Downloaded from trpR SDEC11TP (37). The repressed levels of TSase /2 were equal in strains having E. coli trpR+ and the SDEC11TP or the E. coli W3110 trp operons, although under nonrepressing conditions the trp operon of SDEC11TP produced much more TSase /82 than does that of W3110 because of a partial block in the chorismate-toanthranilate step in the tryptophan pathway of S. dysenterize (13). Thus the trp operator of SDEC11TP, and therefore in all probability the parental S. dysenteriae Shl6 trp operator, can combine with the E. coli trp repressor to achieve normal regulation of trp gene expression.…”

Naturally occurring sites within the Shigella dysenteriae tryptophan operon severely limit tryptophan biosynthesis

“…The structural genes of the S. dysenteriae trp operon are in the same order as in the E. coli operon (7,8); nonetheless, S. dysenteriae strains are deficient in tryptophan synthesis (8). This partial Trp auxotrophy is also shown by transduction hybrids in which the cysB-trp region of S. dysenteriae is introduced into E. coli.…”

“…Members of the genus Shigella are closely related to Escherichia coli. They share susceptibility to some of the same bacteriophages (30), and both intergenic (8) and intragenic (11,40) recombinations have been observed in crosses of S. dysenteriae and E. coli. Measurements of interspecific deoxyribonucleic acid (DNA)-DNA hybridization bolster claims of their kinship (2,31).…”

“…These hybrids grow very slowly on minimal-glucose unless tryptophan is provided. Anthranilic acid will also appreciably stimulate growth, suggesting that it is the conversion of chorismate to anthranilate that is impaired in the tryptophan pathway (8). We describe here experiments to determine the nature and location of the alterations leading to decreased function of the S. dysenteriae trp operon.…”