Recalibrated linkage map of Escherichia coli K-12.

https://mmbr.asm.org/content/mmbr/36/4/504.full.pdf

Linkage map of Escherichia coli strain K-12.

Fourteen deoxyribonucleic acid (DNA) and 10 ribonucleic acid (RNA) methylation mutants were isolated from Escherichia coli K-12 by examining the ability of nucleic acids prepared from clones of unselected mutagenized cells to accept methyl groups from wild-type crude extract. Eleven of the DNA methylation mutants were deficient in 5-methylcytosine (5-MeC) and were designated Dcm. Three DNA methylation mutants were deficient in N6-methyladenine (N6-MeA) and were designated Dam. Extracts of the mutants were tested for DNA-cytosine:S-adenosylmethionine and DNA-adenine:S-adenosylmethionine methyltransferase activities. With one exception, all of the mutants had reduced or absent activity. A representative Dcm mutation was located at 36 to 37 min and a representative Dam mutation was located in the 60-to 66-min region on the genetic map. The Dcm mutants had no obvious associated phenotypic abnormality. The Dam mutants were defective in their ability to restrict λ. None of the mutations had the effect of being lethal.

Isolation of Deoxyribonucleic Acid Methylase Mutants of Escherichia coli K-12

Publisher Summary This chapter reviews that the presence of a variety of minor components has been considered to be one of the typical characteristics of tRNA. Elucidation of the primary sequences of numerous tRNA's has established that minor components are located in specific regions of the tRNA molecule, as arranged in a cloverleaf structure. The minor components in tRNA's is classified into three groups depending upon their locations in the molecule, including: (1) minor components located in the first position of the anticodon, (2) minor components located next to the 3´-OH end of the anticodon, and (3) minor components located in other parts of the tRNA molecule. The chapter discusses that it is possible to increase the content of a minor component by separating short chains of oligonucleotides containing the required minor components. This is possibly the only way to be certain that the component is a part of the tRNA and not an impurity carried through the isolation procedure. When unfractionated tRNA is used as a source of minor components, it is impossible to deduce their locations in the tRNA molecule or to be certain that they are indeed in the tRNA molecule at all. The chapter reviews that the availability of numerous tRNA's enabled to characterize several minor components, and also to correlate the presence of particular minor components with codon recognition of tRNA.

Minor components in transfer RNA: their characterization, location, and function.

Transfer RNA’s role in decoding the genome is critical to the accuracy and efficiency of protein synthesis. Though modified nucleosides were identified in RNA 50 years ago, only recently has their importance to tRNA’s ability to decode cognate and wobble codons become apparent. RNA modifications are ubiquitous. To date, some 100 different posttranslational modifications have been identified. Modifications of tRNA are the most extensively investigated; however, many other RNAs have modified nucleosides. The modifications that occur at the first, or wobble position, of tRNA’s anticodon and those 3¢-adjacent to the anticodon are of particular interest. The tRNAs most affected by individual and combinations of modifications respond to codons in mixed codon boxes where distinction of the third codon base is important for discriminating between the correct cognate or wobble codons and the incorrect near-cognate codons (e.g. AAA/G for lysine versus AAU/C asparagine). In contrast, other modifications expand wobble codon recognition, such as U·U base pairing, for tRNAs that respond to multiple codons of a 4-fold degenerate codon box (e.g. GUU/A/C/G for valine). Whether restricting codon recognition, expanding wobble, enabling translocation, or maintaining the messenger RNA, reading frame modifications appear to reduce anticodon loop dynamics to that accepted by the ribosome. Therefore, we suggest that anticodon stem and loop domain nucleoside modifications allow a limited number of tRNAs to accurately and efficiently decode the 61 amino acid codons by selectively restricting some anticodon‐codon interactions and expanding others.

/pdf/decoding-the-genome-a-modified-view-1iwutacr7a.pdf

Decoding the genome: a modified view.

Isolation of mutants of Escherichia coli lacking 5-methyluracil in transfer ribonucleic acid or 1-methylguanine in ribosomal RNA

Partial purification of ribosomal RNA(m1G)- and rRNA(m2G)methylases from Escherichia coli and demonstration of some proteins affecting their apparent activity

Leif A. Isaksson

Papers

Isolation of mutants of Escherichia coli lacking 5-methyluracil in transfer ribonucleic acid or 1-methylguanine in ribosomal RNA

Partial purification of ribosomal RNA(m1G)- and rRNA(m2G)methylases from Escherichia coli and demonstration of some proteins affecting their apparent activity

Formation in vitro of 1-methylguanine in 23-s RNA from Escherichia coli. The effects of spermidine and two proteins.