tRNA and aminoacyl-tRNA synthetases during differentiation and various functional states of the mammary gland

A few notes on science in Ukraine

As a person who has had a long scientific career in Ukraine, both before and after its re-acquisition of independence thirty years ago, I would like to share my observations with the readership of this Special Issue. By no means are these observations meant to provide a systematic presentation, which requires a different format. Rather, they are highly personal notes, providing snippets of the past and present and a discussion of the future of Ukrainian science. They also allow me to acknowledge my wonderful colleagues and bright students. I am delighted to see that many of them have contributed excellent reviews and original manuscripts to this Special Issue. (I am also keenly aware of the fact that because of the brutal invasion and bombardments by our imperial neighbor, many of my colleagues have been unable to share their latest work). It will be up to this next generation of Ukrainian scientists to develop Biological Sciences in Ukraine in the future.

Influence of cryoprotective agents on protein biosynthesis in Krebs-2 ascites carcinoma and wheat germ cell-free systems

Currently, the cell and tissue storage using the cryoprotective agents are quite common, in particular in reproductive technologies. Meanwhile the issue of safety when applying the CPAs remains open, since even in residual amounts after washing, they can affect the functioning of the most critical metabolic processes of a cell, in particular transcription and translation, which can be of great importance for further life and development of organs, tissues, cells. The goal was to study the effect of penetrating cryoprotective agents glycerol, ME₂SO, ethylene glycol, and non-penetrating PEG-400 on protein synthesizing activity in cell-free systems of Krebs-2 ascites carcinoma and wheat germ. In this study, we compared the effects of ME₂SO, PEG-400, glycerol, and ethylene glycol on protein biosynthesis in cell-free systems according to the incorporation of ¹⁴C-amino acids in total proteins. A reversible suppression of protein biosynthesis in Krebs-2 ascites carcinoma cells and wheat germ cell-free systems by CPAs PEG-400, ethylene glycol, glycerol and ME₂SO was found. This effect is shown to be stipulated by a direct influence of the studied CPAs on translation processes. ME₂SO, glycerol, ethylene glycol and PEG-400 were established to cause the Mg-dependent inhibition of protein biosynthesis in cell-free system of Krebs-2 ascites carcinoma cells in endogenous matrices and wheat germ ones in exogenous matrices. It has been shown that the mechanism of inhibiting action of CPAs on protein biosynthesis in cell-free systems is related to Mg^2+-dependent inhibition of tRNA aminoacylation, which when penetrating Me₂SO, glycerol and ethylene glycol CPAs are used, has a reversible character, and when PEG-400 being a hardly penetrating CPA is applied it is just partially recovered.

The accuracy of poly(U) translation by different eukaryotic tRNAs

In this work we present comparative data on rates of phenylalanine and leucine incorporation into the poly(U) dependent product of cell-free translation by different eukaryotic tRNAs at high Mg2+ concentration. The frequency of translation errors has been found to depend upon the value of the tRNAPhe:tRNALeu ratio and the peculiarities of isoacceptor tRNAsLeu of different origin.

Transfer ribonucleic acids from eleven immunoglobulin-secreting mouse plasmacytomas. Constant and variable chromatographic profiles compared with the myeloma protein sequences

In order to test the concepts that aminoacyl-tRNAs in plasmacytomas may on the one hand modulate the protein synthesized or on the other hand reflect the structure of the synthesized protein, the RPC-5 chromatographic profiles of aminoacyl-tRNAs for all 20 amino acids were studied in tRNA prepared from normal mouse liver and 11 plasmacytomas. The patterns of isoaccepting tRNA were compared with the structure of the myeloma protein being synthesized. The elution profiles of aminoacyl-tRNAs for nine of the amino acids were constant, i.e. they were the same for liver and all plasmacytomas. Significant variability was observed in the profiles of the other 11 families of aminoacyl-tRNAs: asparagine, serine and tryptophan, had peaks of isoaccepting tRNAs found in tumors and not in liver; glutamic acid, histidine and lysine, had different patterns of aminoacyl-tRNAs in plasmacytomas which could be distinguished from the elution profile of liver; and isoleucine, proline, threonine and tyrosine, showed pattern variability in only a few of the tumors. Valyl-tRNA uniquely had one isoacceptor present in liver but absent in the tumors. This variability is thought to be associated with different posttranscriptional modification of the tRNAs rather than regulation of individual tRNA genes in response to particular amino acid sequences in secreted myeloma proteins. Similarily, the lack of correlation of isoacceptors with sequence differences makes the modulation of protein fine structure by tRNA availability unlikely.

Adaptation of the tRNA population of maize endosperm for zein synthesis

Maize endosperm, 30 days after pollination is actively synthesizing zein, a storage protein containing high amounts of glutamine. leucine and alanine. Endosperm tRNAs have a higher accepting activity than embryo tRNAs for these three amino acids, but not for some other (control) amino acids. This increase in accepting activity is accompanied by a change in the distribution of the isoaccepting tRNA species corresponding to these three amino acids, but not of the isoacceptors corresponding to some other (control) amino acids. These results are in favor of the theory of functional adaptation of tRNA population.

A genetic study of erythrocyte arginine-tRNA synthetase activity in man

To search for evidence of genetic variation among the aminoacyl-tRNA synthetases, a semi-automated assay procedure employing a Technicon AutoAnalyzer was used to measure erythrocyte arginine-tRNA synthetase activity in samples obtained from normal human twins of various ages. Variation in enzyme activity within the older DZ twins was five times that of the MZ twins suggesting the existence of genetically determined variation in enzyme activity. Higher enzyme activity was observed in newborn DZ unlike-sexed twins than in like-sexed twins for either zygosity. Possible explanations for this observation are discussed.

Limitation of reticulocyte transfer RNA in the translation of heterologous messenger RNAs

The effect of various tRNAs on protein synthesis was investigated using a tRNA-dependent cell-free system from Ehrlich ascites cells. Ascites cell tRNA and rabbit liver tRNA were found to promote efficient translation of globin mRNA, oviduct mRNA, and encephalomycarditis (EMC) viral RNA. In contrast, reticulocyte tRNA participated efficiently only in the translation of globin mRNA; the translation of oviduct mRNA AND EMC viral RNA in the presence of reticulocyte tRNA resulted in the synthesis of relatively few large mature proteins and the accumulation of discrete, smaller polypeptides. These results suggest that isoaccepting tRNA species required for the synthesis of ovalbumin and EMC viral protein (but not hemoglobin) are probably functionally absent in reticulocyte tRNA, causing a premature, nonrandom termination of synthesis of these proteins. This provides preliminary evidence that variations in tRNA populations, frequently observed between different cell types, are large enough to define and perhaps regulate the proteins that the cell is capable of synthesizing.

Mouse histidyl-tRNAs during pregnancy. Differentiation of activity profiles within and between organs

Optimal conditions for in vitro formation of His-tRNA were established. Transfer RNA of maternal mouse organs and total embryo at 13 and 17 days of pregnancy was acylated in vitro with [3H] or [14C] histidine and examined by reversed-phase plaskon chromatography. Most tissues show different radioactive profiles reflecting a varying activity of six to eight isoaccepting His-tRNA species. Quantitative differences in profile were observed for liver tRNA during pregnancy. Profiles of embryo and uterus, kidney, heart and muscle changes less, and that of brain did not change during pregnancy. The significance of these observations with respect to molecular differentiation of His-tRNAs during pregnancy is discussed.

Transfer of serine into polypeptides and myosin by chromatographic species of seryl-transfer ribonucleic acid

The efficiencies of two chromatographic species of [3-H]seryl-tRNA, namely peaks I and II, in cell-free amino acid incorporation were investigated. The maximum yield of polypeptide seems to be the same for the reaction mixtures containing either peak I or peak II, suggesting that the efficiency of both peaks in total protein synthesis is the same. The efficiency of transfer of serine into myosin heavy subunit (myosin H) by peaks I and II was also investigated. Peak II of [3-H]seryl-tRNA transfers three times as much serine into myosin H as peak I.