Nepsilon-acetyllysine transfer ribonucleic acid: a biologically active analogue of aminoacyl transfer ribonucleic acids

Unfractionated Escherichia coli tRNA has been aminoacylated with lysine and preferentially acetylated at the epsilon-amino nitrogen of lysine by reaction with N-acetoxysuccinimide. After treatment with peptidyl-tRNA hydrolase, 90% of the aminoacylated tRNA molecules were Nepsilon-acetyl-Lys-tRNA. Post-ribosomal supernatant enzymes would not deacylate Nepsilon-acetyl-Lys-tRNA in the presence of AMP and PPi, even though such mixed enzymes could acylate, with lysine, tRNA which had been exposed to the acetylation reaction conditions. Poly(rA) stimulated the binding of Nepsilon-acetyl-Lys-tRNA to E. coli ribosomes. At the ribosome and tRNA concentrations used, Nepsilon-acetyl-Lys-tRNA was bound nearly as well as Lys-tRNA at 30 mM Mg2+; at 10 mM Mg2+, the analogue was bound one-half as well as Lys-tRNA. Both Lys-tRNA and Nepsilon-acetyl-Lys-tRNA reacted only slightly with puromycin at either 10 or 30 mM Mg2+. When Lys-tRNAE. coli or Nepsilon-acetyl-Lys-tRNAE. coli were added to rabbit reticulocyte cell-free protein synthesizing incubations, the incorporation of either amino acid into protein was complete within 5 min. The final incorporation level of the analogue was 82% that of the unmodified lysine. After protein synthesized in the presence of Nepsilon-acetyl-[14C]Lys-tRNA had been digested enzymatically to single amino acids, ion-exchange chromatography and paper electrophoresis showed that nearly all of the radioactivity was present as Nepsilon-acetyllysine. Gel filtration of the post-ribosomal supernatant revealed that most of the Nepsilon-acetyllysine radioactivity cochromatographed with tetrameric hemoglobin.

Acetylcholine and lobster sensory neurones

Experiments are presented in support of the hypothesis that acetylcholine functions as a sensory transmitter in the lobster nervous system.1. Several different peripheral sensory structures incorporate radioactive choline into acetylcholine. The preparation most enriched in sensory as opposed to other nervous elements (the antennular sense organs of the distal outer flagellum) does not incorporate significant amounts of glutamate, tyrosine or tryptophan into any of the other major transmitter candidates.2. There is a parallel between the distribution of the enzyme choline acetyltransferase and the proportion of sensory fibres in nervous tissue from many parts of the lobster nervous system.3. Isolated sensory axons contain at least 500 times as much choline acetyltransferase per cm of axon as do efferent excitatory and inhibitory fibres.4. Abdominal ganglia and root stumps show a decline in the rate of incorporation of choline into acetylcholine 2 to 8 weeks after severing the first and second roots bilaterally (leaving the connectives and third roots intact). Extracts of the root stumps exhibit a significantly lower level of choline acetyltransferase 2 weeks after this operation.5. Curare and atropine partially block an identified sensory synapse in the lobster abdominal ganglion.

Coding properties of reticulocyte lysine transfer RNA's in hemoglobin synthesis

Two isoacceptor transfer RNA's for lysine were found in rabbit reticulocytes. The codon recognition properties of these isoacceptors were studied in hemoglobin synthesis in a cell-free systemn. The two isoacceptors transferred lysine into different sites in hemoglobin, but showed no preference for one chain over the other. Codon cross recognition was less than 4 percent.

Geriatric admissions to a mental hospital

Recently Kay, Beamish and Roth (1964) have shown that there is only a small fraction of old people with psychiatric disorder being cared for either as hospital in-patients or as residents in Homes. Their investigation was carried out in Newcastle-on-Tyne. They pointed out that various other reports concur with the view that medical services at the present time deal only with the visible part of the “iceberg” of mental disorder and handicap.