Gene Action

Yanofsky, Charles; Lawrence, Patricia

doi:10.1146/annurev.mi.14.100160.001523

Cited by 68 publications

(19 citation statements)

References 68 publications

(100 reference statements)

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“…Results indicate that trpB and trpA can be expressed as a single transcript, similar to what has been observed for the trp operon of other bacteria (53,54). C. trachomatis encodes a putative tryptophan repressor (trpR), which presents the possibility that transcription of the trp genes may be regulated by the tryptophan concentration in the host cell.…”

Section: Discussionsupporting

confidence: 79%

Molecular Basis Defining Human Chlamydia trachomatis Tissue Tropism

Fehlner-Gardiner

Roshick

Carlson

et al. 2002

Journal of Biological Chemistry

159

197

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Here we report the cloning and sequencing of a region of the chlamydiae chromosome termed the "plasticity zone" from all the human serovars of C. trachomatis containing the tryptophan biosynthesis genes. Our results show that this region contains orthologues of the tryptophan repressor as well as the ␣ and ␤ subunits of tryptophan synthase. Results from reverse transcription-PCR and Western blot analyses indicate that the trpBA genes are transcribed, and protein products are expressed. The TrpB sequences from all serovars are highly conserved. In comparison with other tryptophan synthase ␤ subunits, the chlamydial TrpB subunit retains all conserved amino acid residues required for ␤ reaction activity. In contrast, the chlamydial TrpA sequences display numerous mutations, which distinguish them from TrpA sequences of all other prokaryotes. All ocular serovars contain a deletion mutation resulting in a truncated TrpA protein, which lacks ␣ reaction activity. The TrpA protein from the genital serovars retains conserved amino acids required for catalysis but has mutated several active site residues involved in substrate binding. Complementation analysis in Escherchia coli strains, with defined mutations in tryptophan biosynthesis, and in vitro enzyme activity data, with cloned TrpB and TrpA proteins, indicate these mutations result in a TrpA protein that is unable to utilize indole glycerol 3-phosphate as substrate. In contrast, the chlamydial TrpB protein can carry out the ␤ reaction, which catalyzes the formation of tryptophan from indole and serine. The activity of the chlamydial Trp B protein differs from that of the well characterized E. coli and Salmonella TrpBs in displaying an absolute requirement for full-length TrpA. Taken together our data indicate that genital, but not ocular, serovars are capable of utilizing exogenous indole for the biosynthesis of tryptophan.

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Section: Discussionsupporting

confidence: 79%

Molecular Basis Defining Human Chlamydia trachomatis Tissue Tropism

Fehlner-Gardiner

Roshick

Carlson

et al. 2002

Journal of Biological Chemistry

159

197

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“…The original hypothesis oftranslational suppression of missense mutations (1)(2)(3) proposed the general nature of tRNA involvement. To date, a variety of specific molecular alterations have been found to result in tRNA-mediated suppression.…”

Section: Methodsmentioning

confidence: 99%

Nucleotide insertion in the anticodon loop of a glycine transfer RNA causes missense suppression.

Prather¹,

Murgola²,

Mims³

1981

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

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We have determined the nucleotide sequences of two unusual UGG-suppressing glycine tRNAs from Escherichia coli and, as a result, have discovered a new mechanism for the generation of missense suppressors. The suppressor tRNAs translate UGG but not UGA. Each arose as a consequence of spontaneous mutational alteration of glyT, the gene for the GGA/Greading glycine tRNA of E. coli In each mutant tRNA, the change in primary structure involved the insertion ofan adenylate residue on the 3' side of the anticodon and the loss ofa modification of the uridylate residue at the 5' end of the anticodon. A "shift" of the effective anticodon by one nucleotide in the 3' direction can account for the new coding specificity of these tRNAs.(19). Nevertheless, both mutant glyT tRNAs suppressed UGG mutations occurring at the same positions in trpA (19). The conversion of a GGA/G-reading glycine tRNA to a UGG-specific suppressor alters its recognition of two positions of the codon (first and third). But suppressors of this type occur frequently, suggesting that members of this class of UGG suppressor can arise from a single mutational event. We determined the nucleotide sequence ofboth of these tRNAs and discovered a new type of missense suppressor tRNA. MATERIALS AND METHODSThe original hypothesis oftranslational suppression of missense mutations (1-3) proposed the general nature of tRNA involvement. To date, a variety of specific molecular alterations have been found to result in tRNA-mediated suppression. For example, the coding specificity of a tRNA can be altered by a change in the anticodon, either by base substitution (for review, see refs. 4-6) or by loss ofa base modification (7-9). In addition to anticodon changes, nucleotide substitutions in other parts of a tRNA molecule can result in suppression by causing attachment of an incorrect amino acid (5, 10). Moreover, a particular anticodon change was found to alter a tRNA so that it accepts a new amino acid and reads a different codon (11). An especially interesting suppressor tRNA is a mutant form of tRNA rP that can translate the termination codon UGA and the tryptophan codon, UGG (12). This mutant tRNA retains the original anticodon, and its suppressor activity is due to a single base change in the dihydrouracil arm of the molecule. How this change, distant from the anticodon, alters the codon response has not been completely resolved, but a consequent change in the tertiary structure of the molecule has been implicated (13)(14)(15). Other mutational studies (7-9, 16-19) also have indicated the importance oftRNA conformation in determining the specificity of codon response.In a recent report, we described the isolation and initial characterization of translational suppressors of a UGG missense mutation in Eschertichia coli (20). Eleven UGG suppressors were shown by genetic mapping and reversed-phase column chromatography to have alterations in glyT, the structural gene for a species of glycine tRNA. Nine suppressed both UGA and UGG mutations. This result was expe...

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“…The hypothesis of suppression (that is, the mutational but nonreversional alleviation of the effects of a mutation) by a change in the transmission of information from gene to protein was suggested some 28 years ago (1). Although the hypothesis focused mainly on the involvement of mutant tRNAs or altered aminoacyl-tRNA synthetases (2,3), it nevertheless allowed for the involvement of the ribosome or other translational macromolecules (4).…”

mentioning

confidence: 99%

Mutant 16S ribosomal RNA: a codon-specific translational suppressor.

Murgola

Hijazi

Göringer

et al. 1988

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

107

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We have isolated an unusual codon-specific translational suppressor in Escherichia coli. The suppressor resulted from a spontaneous mutation in a chromosomal gene during a selection for suppressors of the auxotrophic nonsense mutation trpA(UGA211). The suppressor allows readthrough of UGA mutations at two positions in trpA and at two sites in bacteriophage T4. It does not, however, suppress amber (UAG) or ochre (UAA) mutations that were tested in both genomes, some of which were at the same positions as the suppressible UGA mutations. The suppressor also does not allow mistranslation of the UGA-related tqpA missense mutations UGG at positions 211 and 234, AGA at 211 and 234, CGA at 211, or UGU and UGC at 234. The suppressor mutation was mapped by genetic procedures to position 89 on the E. coli genetic map. Localization of the suppressor mutation to rrnB was achieved by cloning it in the low-copy-number plasmid pEJM007 by in vivo recombination from the chromosome. Recloning in bacteriophage M13 and subsequent DNA sequence analysis allowed the identification ofthe suppressor mutation as a deletion of the cytidylic acid residue at nucleotide position 1054 of the 16S ribosomal RNA. The mutant EcoRI-Xba I fragment from the suppressor gene was recloned, from M13, in an otherwise wild-type rrnB in the plasmid pEJM007, and UGA suppression was examined. The UGA-suppressing activity of the reconstructed suppressor-containing pEJM007 was indistinguishable from that of the original recombinant suppressorcontaining plasmid. This result demonstrates that the C1054 deletion in 16S rRNA is both necessary and sufficient for UGA suppression. The existence of this mutant suggests an important role for rRNA in codon recognition, at least for accurate polypeptide chain termination.

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Gene Action

Cited by 68 publications

References 68 publications

Molecular Basis Defining Human Chlamydia trachomatis Tissue Tropism

Molecular Basis Defining Human Chlamydia trachomatis Tissue Tropism

Nucleotide insertion in the anticodon loop of a glycine transfer RNA causes missense suppression.

Mutant 16S ribosomal RNA: a codon-specific translational suppressor.

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