Search Results - (Author, Cooperation:D. I. Andersson)

2012-10-23

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

*Evolution, Molecular ; *Gene Amplification ; Gene Dosage ; *Genetic Variation ; Histidine/genetics ; *Models, Genetic ; Mutation ; Salmonella enterica/*genetics ; Selection, Genetic ; Time

2018-05-26

The American Society for Microbiology (ASM)

0066-4804

1098-6596

Biology

Medicine

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

lacZ transcriptional and translational fusions of various lengths showed that the control was exerted mainly at the translational level and required both coding and leader sequences in the btuB transcript. Regulatory mutants with a B12 non-repressible phenotype were isolated and the mutations were shown to be located at several sites within the btuB leader. Analysis of constructs carrying site-directed point mutations, which either destabilized or restabilized a putative RNA hairpin that sequesters the btuB ribosomal binding site, demonstrated that this hairpin was essential for normal repression. Comparison of the S. typhimurium btuB gene with the previously characterized S. typhimurium cbiA and Escherichia coli btuB genes reveals significant similarities as well as differences in the cis-acting sequences required for repression.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Expression of the cob operon is repressed by B12 via a post-transcriptional control mechanism which requires sequence elements within the leader region of the mRNA and the first gene of the operon, the cbiA gene. Here we show that B12 repression of cbiA gene expression occurs at the level of translation initiation through sequestration of the ribosomal binding site (rbs) in an RNA hairpin. Analysis of mutations that destabilize or restabilize the secondary structure demonstrates that folding of the hairpin is essential for repression. The existence of the hairpin was confirmed by a secondary structure analysis of RNA from the wild type and three mutants. Deletions that remove the upstream part of the leader confer a drastic reduction in translation efficiency. This low-level translation is caused by the hairpin, as indicated by the finding that suppressor mutations that destabilize the hairpin restore efficient translation. Thus, the native upstream RNA functions as a translation enhancer and acts to relieve the hairpin's inhibitory effect on translation initiation. The inhibitory effect of the hairpin was confirmed by a ribosomal toeprinting analysis. We propose that the translational control of the cbiA gene mediates repression of the entire cob operon.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

We have identified an anaerobicaily induced promoter for the cobalamin biosynthetic (cob) genes. In a plasmid the Cob promoter showed two of the three types of control of the intact chromosomal Cob operon: anaerobic induction and cAMP stimulation. Cobalamin repression was observed only in promoter fragments which included sequences far downstream of the transcription start site, suggesting that this control is post-transcriptional. One anaerobically induced transcript was identified and its 5′ end was determined. Deletion mapping showed that 60 nucleotides upstream of the start site were sufficient for anaerobic synthesis of this transcript. Upstream of the transcription start site a putative σ70-dependent -10 recognition sequence was identified; however, no consensus -35 region was observed.

Electronic Resource

1617-4623

Springer Online Journal Archives 1860-2000

Biology

Summary We have studied the kinetics of poly(U) translation by three ribosomal ambiguity (Ram) mutants in an in vitro system with performance characteristics similar to those expressed in vivo. The leucine missense frequency supported by Ram ribosomes with tRNA 2 Leu increases between six and twelve-fold over that of wild-type ribosomes, while the corresponding increase with tRNA 4 Leu was between four and eight-fold, depending on the rpsD allele. We have used a steady-state assay for profreading to identify the kinetic lesion responsible for the Ram phenotype. We were unable to detect any difference between Ram and wild-type ribosomes with respect to the initial kinetics of amino-acyl-tRNA selection. All of the increased error rates could be associated with a decreased capacity of these Ram ribosomes to discard non-cognate aminoacyl-tRNA by proof reading.

Electronic Resource