[Interrelation between protein synthesis and nucleo-cytoplasmic transport of messenger RNA in cells of rat livers in different stages of regeneration]. / Vzaimosviaz' sinteza belka i iaderno-tsitoplazmaticheskogo transporta informatsionnoi RNK v kletkakh pecheni krys na raznykh stadiiakh regeneratsii.

Synthesis of nonribosomal RNA was increased 2-2.5-fold in nuclei of rat liver cells at early steps of regeneration /2 days after partial hepatectomy/under conditions of protein synthesis inhibition by means of cycloheximide within 3 hrs. Amount of mRNA, transferred from nuclei into cytoplasm, was also 2-fold higher under these conditions as compared with control cells. The mRNA, transferred from nuclei into cytoplasm under the conditions of cycloheximide treatment of liver cells at early steps of regeneration, did penetrate the polyribosomes although the protein synthesis did not occur on the polyribosomes formed. At the later steps of regeneration /within 5 days after partial hepatectomy/ under the conditions of protein synthesis inhibition by cycloheximide within 3 hrs, formation of nonribosomal RNA was decreased by 40% in liver cell nuclei; amount of mRNA, transferred into cytoplasm, was also decreased by 40%. When the cycloheximide treatment was carried out during 1 hr, synthesis of nonribosomal RNA was increased 1.5-fold in liver cell nuclei at the later steps of regeneration although the amount of mRNA, transferred from nuclei into cytoplasm, was decreased by 30% as compared with the control cells. The data obtained suggest that during rat liver tissue regeneration a change occurred in the molecular mechanisms linking translation, biosynthesis and nuclear-cytoplasmic transport of mRNA of "tumoral" type/at early steps of regeneration/ or "normal type"/ at later steps of regeneration.

[Changes in the mechanisms controlling mRNA stability during the process of liver regeneration in rats]. / Smena mekhanizmov, kontroliruiushchikh stabil'nost' mRNK, v protsesse regeneratsii pecheni krys.

If the protein biosynthesis was inhibited by cycloheximide, an elevated degradation of total mRNA, including mRNA of membrane-bound and free polyribosomes, occurred in the liver cells at early steps of regeneration, within 48 hrs after partial hepatectomy. Simultaneously, distinct increase in activity of alkaline RNAases was observed in cytoplasm as well as of endo-RNAase--in the membrane-bound and free polyribosomes. As shown in experiments with-p-chloromercuribenzoate, the increase in activity of alkaline RNAases in treatment with cycloheximide was due to a decrease in content of short-living proteins, which are inhibitors of RNAases, in cytoplasm of 48 hr regenerating liver cells. At the later period of liver tissue regeneration within 5 days after partial hepatectomy), under conditions of inhibition of protein biosynthesis using cycloheximide, stabilization of mRNA from membrane-bound polyribosomes was observed while the mRNA from free polyribosomes was in a state of degradation. Within this period the endo-RNAase activity was markedly decreased in membrane-bound polyribosomes but the enzymatic activity was increased in free polyribosomes. The mechanisms, controlling the mRNA stability, were apparently changed during the regeneration of rat liver tissue.

[Nucleo-cytoplasmic mRNA transport in liver rat and hepatoma cells following suppression of protein synthesis by cycloheximide]. / Iaderno-tsitoplazmaticheskii transport mRNK v kletkakh pecheni i gepatomy krys pri podavlenii belkovogo sinteza tsiklogeksimidom.

Specific radioactivity of uridylic nucleotide pool was found to be 2-2.5-fold higher in rat liver cells treated with cycloheximide within 3 hrs as compared with the control liver cells. Cycloheximide did not affect the specific radioactivity of the nucleotide pool in cells of Zajhdel ascites hepatoma. Nuclear-cytoplasmic transport of mRNA was decreased by 40-60% in rat liver cells after inhibition of protein synthesis by cycloheximide within 3 hrs. In this case, synthesis of non-ribosomal RNA was also decreased by 20-30% in nuclei. Treatment with cycloheximide caused 2.5-3-fold increase in synthesis of non-ribosomal nuclear RNA in rat cells of Zajhdel ascites hepatoma; amount of mRNA, transported from nucleus into cytoplasm, was also 2-3-fold higher in the tumoral cells as compared with controls. Under conditions of cycloheximide action, mRNA, which is transported from nuclei, continued to enter the polyribosomes of Zajhdel ascites hepatoma cells at the normal rate, although the protein synthesis did not occur in these polyribosomes.

[Change in RNase activity in rat liver cells in cycloheximide protein synthesis inhibition]. / Izmenenie aktivnosti RNK-az v kletkakh pechenie krys pri ingibirovanii belkovogo sinteza tsiklogeksimidom.

Administration of cycloheximide to rats does not change the activity of acid and alkaline RNAases in the cytoplasm of hepatocytes. At the same time cycloheximide-induced inhibition of protein synthesis leads to a fall in the activity of RNAase of microsomes and membrane-bound polyribosomes. The activity of RNAase of free polyribosomes of hepatocytes rises considerably under the action of cycloheximide.

[mRNA breakdown in tumor cells in vivo under cycloheximide protein synthesis inhibition]. / Razrushenie mRNK v opukholevykh kletkakh in vivo pri ingibirovanii belkovogo sinteza tsiklogeksimidom.

Amoung of prelabelled mRNA was unaltered in Zajhdel ascites hepatoma of rat cells within 3.5-4 hrs under conditions of treatment with actinomycin D. Due to combined effect of actinomycin D and cycloheximide the content of mRNA in the hepatoma cells was rapidly decreased. Degradation of mRNA occurred in membrane-bound polyribosomes, free polyribosomes and in cytoplasmic mRNP-particles /informosomes/ as a result of the effect of cycloheximide. Simultaneously with these phenomena, distinct increase in activity of acid and alkaline RNAases was observed in cytoplasma of the hepatoma cells; activity of endoRNAase from membrane-bound and free polyribosomes of the hepatoma was also markedly increased. Cycloheximide did not affect the activity of polynucleotide phosphorylase in polyribosomes of the hepatoma cells. Labile proteins, responsible for inhibition of RNAses appeart to participate in regulation of mRNA stability in malignant cells.

[Stabilization of polyribosomal mRNA in rat liver cells under protein synthesis inhibition by cycloheximide]. / Stabilizatsiia mRNK poliribosom v kletkakh lecheni krys pri ingibirovanii belkovogo sinteza tsiklogeksimidom.

It was found that in the course of centrifugation of the postmitochondrial fraction from rat liver in the sucrose concentration gradient, mRNA located in the EDTA-resistant structures sedimented together with polyribosomes. The same structures were detected in the polyribosomal fraction of liver cells after injection of ethionine to the animals. Centrifugation of polyribosomes through a layer of 2.0 M sucrose at 105 000 g for 4 hrs and subsequent centrifugation through a layer of 1.0 M sucrose resulted in the disappearance of the complexes from the polyribosomal fraction. Evidence for the absence of destruction of labelled polyribosomal mRNA in liver cells following the injection of cycloheximide were obtained. Actinomycin D also stabilized polyribosomal mRNA in liver cells, however, in a much lesser degree as compared to cycloheximide. Possible mechanisms of the stabilizing effects of cycloheximide and actinomycin D on polyribosomal mRNA in liver cells are discussed.

[Metabolism of mRNAs of membrane-bound and free-polyribosomes from rat liver cells during translation and its inhibition]. / Metabolizm informatsionnykh RNK membranosviazannykh i svobodnykh poliribosom v kletkakh pecheni krys v protsesse transliatsii i pri ee ingibirovanii

Metabolism of membrane-bound and free polyribosomal RNAs was studied under conditions of suppressed synthesis of rRNA induced by small doses of actinomycin D. Besides actinomycin D, cycloheximide was used to suppress the protein synthesis. It was demonstrated that administration of cycloheximide and actinomycin D to rats resulted in a stabilization of membrane-bound polysomal mRNA in liver cells. Simultaneously with the action of those antibiotics, free polysomal mRNA was shown to degrade in exactly the same way as in the liver of control animals. Study of poly-A-containing mRNA metabolism showed that during the first hour following rat labelling specific radioactivity of membrane-bound polysomal mRNA was higher than that free polysomal mRNA. Within the interval of 1-5 hours after labelling specific activity of mRNAs of both polysomal fractions reached the same level. In the cell-free system of protein synthesis the membrane-bound polysomes of rat liver cells appeared to be much more active as compared to the free ones. The addition of poly-U matrix to the cell-free system of protein synthesis significantly stimulated the free polysomes activity during 14C-phenylalanine incorporation into polypeptides. Interrelationship of mRNAs of membrane-bound and free polysomes in eucaryotic cells is discussed.

[Interrelationship between protein synthesis and mRNA metabolism in rat liver cells]. / Vzaimosviaz' belkovogo sinteza i metabolizma informatsionnoi RNK v kletkakh pecheni krys

It is demonstrated that RNA isolated from polyribosomes and postmitochondrial fraction of rat liver cells and bound to nitrocellulose filters (Milliport) represent mRNA. RNA taken from the nitrocellulose filters sedimented in sucrose concentration gradient with a wide peak within the range of 18--6S, attaining a maximum at 12S. The (A+U)/(G+C) ratio of this RNA was equal to 1.04. On the other hand, the same ratio for rRNA was 0.64. Specific radioactivity of polysomal mRNA containing poly-A sequences, was significantly lower at 14-hour labelling with 14C-orotate than at 4-hour labelling (control). Inhibitors (cycloheximide, puromycin, ethionine, actinomycin D) stabilized polysomal mRNA. Specific radioactivity of postmitochondrial fraction mRNA was higher at 14-hour labelling than at 4-hour labelling. Specific radioactivity of postmitochondrial fraction mRNA during protein synthesis blocking by different inhibitors was comparable to those of control animals. It is hypothesized that active translation is necessary for the initiation of rat liver mRNA degradation.

[Rate of ribosome movement along messenger RNA in E. coli under normal and inhibited translation]. / O skorosti dvizheniia ribosom vdol' informatsionnoi RNK u E. coli pri normal'noi transliatsii i pri ee ingibirovanii

Considerable decrease of polysome number (22% as compared with 48% in normally grown culture) was observed under methionine starvation of E. coli Hfr (Met-)culture . At the same time the amount of 70S ribosomes increased up to 32%, while it was 2--6% in the control, the content of free ribosome subunits (50S+30S) being stable. The number of polysomes was the same (congruent to 50%) both in the control culture and under inhibition of protein synthesis in E. coli Hfr(Met-) cells with chloramphenicol, the content of 70S ribosomes was increased (30%) like in the case of methionine starvation, and the amount of free ribosome subunits was decreased (24% as compared with 46% in the control). The rate of ribosome movement in polysomes in the presence of chloramphenicol is comparable with that in the control. The rate of ribosome movement along mRNA under methionine starvation in 1.6 times lower than in normally grown E.coli culture. The level of (14)C-leucine incorporation into newly synthesizing polysome proteins under chloramphenicol inhibition of protein synthesis and methionine starvation comprised 20% and 12% of the incorporation level inthe control respectively. It suggested that ribosomes under inhibition of protein synthesis by chloramphenicol or amino acid starvation continue their movement along mRNA with the rate comparable with that in the control. However in this case no peptide bonds are formed ("abortive" translocation).

[Messenger RNA metabolism in E. coli under amino acid starvation conditions]. / Obmen informatsionnoi RNK u E. coli v usloviiakh aminokislotnogo golodaniia

In E. coli Hfr Kavalli (met-) turnover of mRNA was studied in normal state and in methionine deficiency. This strain of E. coli was shown to have the 'loose' type of regulation of RNA synthesis (RC-). Without methionine in E. coli Hfr the rate of the protein synthesis was about 7-8% of that found in the control culture. In studies of the total mRNA turnover the half-life of matrices was equal to 2 min at 37degree, if a medium did not contain methionine; the same value was observed in the control culture. At the same time in methionine starvation an increase in amount of rapidly labelled RNA was observed; the RNA remained stable under simultaneous effect of actinomycin D. This rapidly labelled, stable RNA was the messenger-RNA, associated with cytoplasmic membranes. The hypothesis is advanced that membrane-associated and cytoplasmic RNA are those two types of matrices, which differed in their stability when the protein synthesis was inhibited.

[Stability of the polyribosomes of Blakeslea trispora Thaxter during normal translation, its stimulation and inhibition]. / Stabil'nost' poliribosom u Blakelea trispora thaxter pri normal'noi transliatsii, pri ee stimuliatsii i ingibirovanii

beta-Ionone is found to stimulate considerably carotinoids synthesis in Blakeslea trispora. The stabilization of carotene-synthesizing ability of B. trispora in the presence of beta-ionine under prolonged incubation time is observed. Stabilization of polyribosomes in the presence of beta-ionine is observed when studying polyribosome content in B. trispora. A hypothesis is expressed on the existence of biochemical "receptors" as a linkage between synthesized protein and destroying mRNA.

[The mechanism of action of trisportic acids on the carotene-synthesizing enzymes of the (-) strain of Blakeslea trispora]. / Mekhanizm deistviia trisporovykh kislot na karotinsinteziruiushchie fermenty (-) shtamma Blakeslea trispora

Trisporic acids were found to increase the content of carotene, protein, and RNA in the (-)strain of Blakeslea trispora. Trisporic acids are inductors of the synthesis of carotenogenous enzymes as was found in experiments with the inhibitor of transcription (cycloheximide) and translation (actinomycin D). Trisporic acids stimulate the formation of neutral fractions of the sex hormone, the process being regulated presumably at the level of posttranscription control.