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G Keith

Publications and source records attributed to G Keith.

At least 145 records · Page 8Linked to original sources
PubMed1976

Specific cleavages of pure tRNAs by plumbous ions.

After renaturation some pure tRNAs were submitted to the action of lead acetate 1 . 10(-3) M at pH 7.3 and at 37 degrees C in the presence of either 1 M or 0.5 M NaCl. These tRNAs were specifically cleaved by Pb2+. The exact cleavage points were determined by analysing the oligonucleotides obtained from three yeast tRNAs. In 1 M NaCl, tRNA(Phe) is cleaved after the hUp17 and partially cleaved after Cp73. In 0.5 M NaCl, there are cleaveages after hUp16, hUp17 as well as a partial one after pGP1. In 1 M NaCl tRNA(Asp) is not cleaved, whereas in 0.5 M NaCl 50% of the molecules are cleaved in the anticodon region after Up35, 14% after hUp19 and 6% after hUp16. In 1 M NaCl tRNA(Val) is cleaved in the hU loop: 40% after hUp16 and 60% after CP17. The action of lead on five other pure tRNAs was studied on the analytical scale only, by polyacrylamide gel electrophoresis. They could be classified into two familites, one cleaved mainly in the hU loop, the other in the anticodon loop. The minimal concentrations of Pb2+ required for cleavage were determined for several tRNAs, the most sensitive of which, yeast tRNA(Val), being still cleaved with a concentration of 5 . 10(-6) M in 0.15 M NaCl. Although the cleavage often occurs after hUp, poly (hU) is less sensitive than poly(U). This and other results indicate that cleavages depend more on the conformation than the sequence of the polynucleotide chain, bends in the tertiary structure being lead-sensitive sites. Finally, the amino acid acceptance activities of cleaved tRNA(Phe) and tRNA(Asp) were determined.

Anticodon↗
PubMed1976

An improved method for the separation and quantitation of the modified nucleosides of transfer RNA.

A method is described which allows a very efficient determination of the modified nucleosides of tRNA. The technique involves enzymatic degradation of the tRNA to nucleosides at pH 7.6 and their separation by two-dimensional thin-layer chromatography on cellulose-coated aluminum foils. Based on the analysis of two mammalian tRNAs it is shown that the technique is suitable for the determination of chemically unstable nucleosides as well as the ribose-methylated compounds. At least 36 of the 45 known modified nucleosides can be separated and quantitatively determined by the method described. This procedure is especially suitable for the estimation of the nucleoside composition of unlabeled tRNAs as well as for studying the post-transcriptional modifications of tRNA.

Aluminum↗