The sequence of four structural and two regulatory methionine genes in the Salmonella typhimurium linkage map

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The systems which transport methionine in Salmonella typhimurium LT2 have been studied. Fourteen mutants, isolated by three different selection procedures, had similar growth characteristics and defects in the specific transport process showing a Km of 0 . 3 ,~~ for L-methionine, and therefore lack the high-affinity, metP transport system. The sites of mutation in four of the mutants were shown by P1-mediated transduction to be linked (0-3 to 1.1 %) with a proline marker located at unit 7 on the S. typhimurium chromosome. The high-affinity system was subject to both repression and transinhibition by methionine, and it may also be regulated by the metJ and metK genes. There appeared to be at least two additional transport systems with relatively low affinities for methionine in the metP763 mutant strain, with apparent Km values for methionine of 24 ,UM and approximately 1.8 mM. The latter system, with a very low affinity for methionine, was inhibited by leucine. In addition, methionine inhibited leucine transport, suggesting that one of the low-affinity methionine transport systems may actually be a leucine transport system.

Section: Introductionmentioning

confidence: 99%

Methionine Transport in Salmonella typhimurium: Evidence for at Least One Low-affinity Transport System

Ayling¹,

Mojica-A²,

Klopotowski³

1979

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“…Smith, were propagated, assayed and maintained as described by Smith (1961). Transduction and conjugation analysis were as described by Ayling & Chater (1968).…”

mentioning

confidence: 99%

Methionine Transport in Wild-type and Transport-defective Mutants of Salmonella typhimurium

Ayling

Bridgeland

1972

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-2 p~) .Competition studies have shown that the permease has little or no affinity for the other L-amino acids commonly found in proteins. Methionine uptake was competitively inhibited by the growth inhj bitory analogues DLethionine, a-methyl-DL-methionine and DL-methionhe-DL-sulphoximine. Mutants resistant to a-methyl-methionine and methionine sulphoximine have been isolated which were severely defective in the niethionine specific permease. Two of these mutants, metP760 and rnetP761, mapped away from all previously located methionine structural and regulatory genes.

“…All other strains were derived from Salmonella typhimurium strain L T~. Those previously described were: mefA15, A54, A229 and A309, metAz2tryB2, and metA43puvE1 I (Smith & Childs, 1966) ; argFrrr, argFrrrmetI708, metA746metI706, metB23metI708 and metBz3metJ744 (Ayling & Chater, 1968) ; metI701, I702, 1703, 1704, 1705, 1706, 1708, and I712 (Lawrence et al 1968); argF111rec-30rpyr (Chater,197oa), and metBz3metK747 (Chater, 1969). Mutant met1749 was provided by P. D. Ayling, and strain metA7 was obtained by transduction of the double mutant metA7cysAzr (Smith & Childs, I 966) to cysteine independence.…”

Section: Mediamentioning

confidence: 99%

“…Transduction and recombinant analysis were as described by Ayling & Chater (1968), except in the deletion analysis of met1 mutants, when the normal method would have involved the use of too much expensive a-methylmethionine. Instead, use was made of the methionine excretion of metl mutants, by analogy with a similar study of histidine feedback inhibition-resistant mutants of Salmonella typhimurium (Sheppard,I 964).…”

Section: Mediamentioning

confidence: 99%

“…Preliminary deletion mapping experiments led Lawrence et al (I 968) to speculate that metA and metZ might be separate cistrons, metA specifying a catalytically active subunit of the enzyme and met1 a regulatory subunit. This idea was reinforced by the data of Ayling & Chater (1968), who found that three independent pairs of metA and Z mutations had the same orientation relative to outside markers.…”

mentioning

confidence: 93%

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A Genetical Study of the Feedback-sensitive Enzyme of Methionine Synthesis in Salmonella typhimurium

Chater

Rowbury

1970

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S U M M A R YThe homoserine-0-transsuccinylase activity of three kinds of methionineexcreting mutants of Salmonella typhimurium was examined. In a metl mutant the enzyme was resistant to inhibition by methionine or its analogue a-methylmethionine. Feedback inhibition in a metJ and a metK strain was normal. rnetl was dominant to metI+ only when coupled in the cis position with the wild-type allele of the closely-linked metA (homoserine-0-transsuccinylase) gene, and a deletion analysis of nine met1 mutations showed that they were all located within the metA gene. Thus both the regulatory and catalytic sites of homoserine-0-transsuccinylase are specified by a single polypeptide species. An estimate was made of the length of the metA gene, based on recombination data.