[107] Enzymes involved in the biosynthesis of tryptophan

Smith, Oliver H.; Yanofsky, Charles

doi:10.1016/s0076-6879(62)05315-x

Cited by 184 publications

(95 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Minimal medium for corynebacteria (MMC) was as described by Kaneko and Sakaguchi (16). E. coli strains were grown in Luria broth (LB) or Luria agar (LA) (35) or in VB minimal medium (40) at 37°C, except when other conditions are specified.…”

Section: Materuils and Methodsmentioning

confidence: 99%

Transcriptional analysis and regulatory signals of the hom-thrB cluster of Brevibacterium lactofermentum

et al. 1994

View full text Add to dashboard Cite

Two genes, hom (encoding homoserine dehydrogenase) and thrB (encoding homoserine kinase), of the threonine biosynthetic pathway are clustered in the chromosome of Brevibacterium lactofermentum in the order 5' hom-thrB 3', separated by only 10 bp. The Brevibacterium thrB gene is expressed in Escherichia coli, in Brevibacterium lactofermentum, and in Corynebacterium gluamicum and complements auxotrophs of all three organisms deficient in homoserine kinase, whereas the Brevibacterium hom gene did not complement two different E. coil auxotrophs lacking homoserine dehydrogenase. However, complementation was obtained when the homoserine dehydrogenase was expressed as a fusion protein in E. coil. Northern (RNA) analysis showed that the hom-thrB cluster is transcribed, giving two diferent transcripts of 2.5 and 1.1 kb. The 2.5-kb transcript corresponds to the entire cluster hom-thrB (i.e., they form a bicistronic operon), and the short transcript (1.1 kb) originates from the thrB gene. The promoter in front of hom and the hom-internal promoter in front of thrB were subcloned in promoter-probe vectors of E. col and corynebacteria. The thrB promoter is efficiently recognized both in E. coil and corynebacteria, whereas the hom promoter is functional in corynebacteria but not in E. coil. The transcription start points of both promoters have been identified by primer extension and S1 mapping analysis. The thrB promoter was located in an 87-bp fragment that overlaps with the end of the hom gene. A functional transcriptional terminator located downstream from the cluster was subcloned in terminator-probe vectors.Threonine is synthesized from aspartic acid in five enzymatic reactions. The initial two reactions which convert aspartic acid to aspartate-13-semialdehyde are common to the lysine pathway. Conversion of aspartate-p-semialdehyde into homoserine (catalyzed by homoserine dehydrogenase [HD]) is common for threonine and methionine biosynthesis. Homoserine is converted into threonine by the action of two other enzymes, homoserine kinase (HK) and threonine synthase (TS).In Escherichia coli, the genes encoding four of the five enzyme activities involved in threonine biosynthesis are clustered together in the thrABC operon. The thrA gene encodes the bifunctional enzyme aspartokinase-HD (AKI-HDI), whereas thrB and thrC encode HK and TS, respectively (7,20). In corynebacteria there is one monofunctional HD (17), whereas in E. coli there are two isoenzymes (HDI and HDII, respectively) that form part of bifunctional polypeptides AKI-HDI and AKII-HDII.We previously cloned and sequenced the Brevibacterium lactofermentum hom gene encoding the monofunctional HD (26) and the thrB gene encoding HK (24,25) and showed that both are clustered. The thrC gene encoding TS was found to be at a separate position in the chromosome (21). An arrangement of the three genes identical to that in B. lactofermentum was found in Corynebacterium glutamicum (12,13,32). These two microorganisms are closely related nonpathogenic corynebacteria (7a). The nuc...

show abstract

Section: Materuils and Methodsmentioning

confidence: 99%

Transcriptional analysis and regulatory signals of the hom-thrB cluster of Brevibacterium lactofermentum

et al. 1994

View full text Add to dashboard Cite

show abstract

“…R. meliloti tip mutants were assigned to genetic classes based trations of tryptophan (3 ,ug/ml) (25); the characteristics of other mutants within the same complementation group and complementation of defined P. aeruginosa PAO trp mutants have already been described (1,15). trpC mutants were differentiated from trpD mutants on the basis of assay of phosphoribosyltransferase as described by Smith and Yanofsky (27). Genetic manipulations, transposon mutagenesis, and Southern hybridization.…”

Section: Methodsmentioning

confidence: 99%

Rhizobium meliloti mutants unable to synthesize anthranilate display a novel symbiotic phenotype

et al. 1992

View full text Add to dashboard Cite

Analyses of Rhizobium meliloti trp auxotrophs suggest that anthranilate biosynthesis by the R. meliloti trpE(G) gene product is necessary during nodule development for establishment of an effective symbiosis. trpE(G) mutants, as well as mutants blocked earlier along this pathway in aromatic amino acid biosynthesis, form nodules on alfalfa that have novel defects. In contrast, R. meliloti trp mutants blocked later in the tryptophan-biosynthetic pathway form normal, pink, nitrogen-fixing nodules. trpE(G) mutants form two types of elongated, defective nodules containing unusually extended invasion zones on alfalfa. One type contains bacteroids in its base and is capable of nitrogen fixation, while the other lacks bacteroids and cannot fix nitrogen. The trpE(G) gene is expressed in normal nodules. Models are discussed to account for these observations, including one in which anthranilate is postulated to act as an in planta siderophore.

show abstract

“…Therefore, a comparison of the number of ribosomes that translate trpB (giving the B protein) with those that continue through trpA (giving the A protein) determines the transmission efficiency. Measurement of the trpB (or trpA) product is performed enzymatically in extracts of log-phase cells by fully complementing it with exogenous trpA (or trpB) product (12) to generate tryptophan synthase. Various altered proteins all bind to the B protein and activate it (for synthesis of tryptophan from indole) to the same extent (25).…”

Section: A CC G G a T T C T A A C T Cc G G C Cc G G T C T C T A mentioning

confidence: 99%

Construction of a composite tRNA gene by anticodon loop transplant.

Yarus¹,

McMillan²,

Cline³

et al. 1980

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

By using sites for the restriction nuclease Hpa II, the information for the anticodon stem and loop of an altered Su+2 amber suppressor tRNA (a mutant of tRNAG-n) has been transplanted to a specially prepared tRNATrP gene, which lacks its homologous anticodon stem and loop sequence. The resulting tRNA gene was cloned under lac operator-promoter control. The result is a functional, hybrid, amber-suppressor tRNA that can exhibit a moderately high efficiency in translation. It appears less efficient, however, than Su+7 tRNA, the amber suppressor that results from a direct anticodon mutation in tRNATrP. As judged by its suppressor spectrum, which is almost identical to the spectra of Su+2 and Su+7, the recomposed tRNA inserts glutamine at amber sites. This experiment is the prototype of a series of constructions that examine the role of the nucleotides in the anticodon region.

show abstract

[107] Enzymes involved in the biosynthesis of tryptophan

Cited by 184 publications

References 5 publications

Transcriptional analysis and regulatory signals of the hom-thrB cluster of Brevibacterium lactofermentum

Transcriptional analysis and regulatory signals of the hom-thrB cluster of Brevibacterium lactofermentum

Rhizobium meliloti mutants unable to synthesize anthranilate display a novel symbiotic phenotype

Construction of a composite tRNA gene by anticodon loop transplant.

Contact Info

Product

Resources

About