An improved method for the quantitative isolation of rat liver nuclear RNA polymerases

Hepatic nuclear free and engaged RNA-polymerases in young rats pretreated with 3-methylcholanthrene

In 3-methylcholanthrene (3-MC)-pretreated young rats the free and engaged RNA polymerases were investigated in detail both in the nucleolar and nucleoplasmic fractions. Both functional forms of the nucleolar RNA polymerase (A) show a great stimulation. The maximum increase of the free form up to 235% compared with controls is obtained 24 h after 3-MC administration. The engaged fraction reaches its maximum later. The extranucleolar RNA polymerase (B) in its engaged form shows the maximum effect (160%) after 24 h, whereas the free form is at first diminished and later on increases steadily. The activation of RNA polymerase A and the interconversion process between the free and engaged form of RNA polymerase B seem to play a significant role in the 3-MC-mediated induction.

RNA synthesis by nuclei and nucleoli from ischemic liver cells

Nuclei and nucleoli were isolated from rat livers subjected to an interruption of the blood supply for periods of different duration, as well as after restoration of the blood supply. They were assayed for RNA synthesis under conditions of diverse ionic strengths, and in the presence of an exogenous template, such as poly d (A-T), and actinomycin to inactivate the endogenous template; alpha-amanitin was made used of to distinguish polymerase I and polymerase II dependent RNA synthesis. Nuclei and nucleoli from ischemic livers showed a severe impairment of RNA synthesis, which is likely to be due to decreased initiation frequency of the engaged polymerases, while free polymerases were essentially unchanged. Both form I and II polymerase were equally involved. After restoration of the blood supply RNA synthesis recovered with an overshooting well above normal levels of activity, lasting for at least 24 hours. Increased RNA synthesis was not followed by thymidine incorporation into DNA.

RNA synthesis in isolated nuclei of lactating mammary cells in presence of unmodified and mercury-labeled CTP

Isolated nuclei of lactating mouse mammary gland were capable of supporting DNA-dependent RNA synthesis in vitro in presence of unmodified and mercurated CTP (Hg-CTP) at high ionic condition at 25 degrees C. In presence of unmodified CTP, [3H]UMP incorporation into RNA increased linearly upto 180 min. The kinetic pattern of the reaction and the rate of RNA synthesis were essentially similar when CTP was replaced by Hg-CTP. Both in unmodified and Hg-CTP containing reactions, 70-80% of RNA synthesis was inhibited by alpha-amanitin. Presence of poly(A) in a small portion of the in vitro synthesized messenger-like RNA was detectable by oligo(dT) cellulose chromatography. Both poly(A)+ and poly(A)- RNAs sedimented with a clear peak around 15S region in a formamide-sucrose denaturing gradient. The Hg-RNA after separation from endogenous nuclear RNA by SH-agarose affinity column chromatography also sedimented around 15S region in a formamide-sucrose gradient. The Hg-RNA synthesized in the isolated mammary cell nuclei in vitro should now permit monitoring hormonal regulation of specific gene (casein) transcription in the mammary cells by molecular hybridization of the Hg-RNA with cDNA to casein mRNA.

Purification of class A, B, and C DNA-dependent RNA polymerases from chicken embryos

Crude nuclei were isolated from trunks of 13-day-old chicken embryos under conditions which prevent leakage of RNA polymerases from nuclei. RNA polymerases were solubilized by subsequent incubation in alkaline buffer and sonication at high salt concentration. Purification of RNA polymerases A, B, and C was achieved by conventional column chromatographic procedures. RNA polymerase B was freed from an UTP:polynucleotidyl exotransferase by chromatography on a tRNA-Sepharose column. Purified RNA polymerase A contained six putative subunits with molecular weights 190 000 (A1), 117 000 (A2), 57 000 (A3), 50 000 (A4), 25 000 (A5), 19 000 (A6); RNA polymerase B contained eight putative subunits with molecular weights 98 000 (B2'), 86 000 (B2''), 155 000 (B3), 44 000 (B4), 31 000 (B5), 28 000 (B6), 26 000 (B7), 19 000 (B8); RNA polymerase C contained nine putative subunits with molecular weights 170 000 (C1), 117 000 (C2), 84 000 (C3), 60 000 (C4), 49 000 (C5), 36 000 (C6), 33 000 (C7), 22 000 (C8), 19 000 (C9).

Effect of tryptophan on hepatic nuclear free and engaged RNA-polymerases in young and adult rats

Whereas in young rats (2 weeks old), administration of typtophan produced marked enhancement in the activity of both engaged and free polymerases of nuclei, in adult rats (10 weeks old) only the engaged polymerases showed higher activities following tryptophan force-feeding.

The relationship between the activities of different pools of RNA polymerases I and II during PHA-stimulation of human lymphocytes

Following PHA-stimulation of lymphocytes in culture, it is known that nuclear RNA synthesis and the amount of extractable RNA polymerase activity rise in these cells. The relationship between these two phenomena has been examined. Using an in vitro assay system which discriminates between polymerase activity which is "engaged" in nuclear RNA synthesis and a pool of "free" enzyme, the data suggest that the factors regulating the interaction between these two pools of enzyme activity are different for forms I and II RNA polymerases.

RNA metabolism and poly(A) distribution in mouse liver following administration of dimethylnitrosamine

Dimethylnitrosamine (DMNA) strongly inhibited RNA synthesis in mouse liver under conditions when the nucleotide pattern, rate of nucleotide synthesis and phosphorylation ratio were unaffected. (An unidentified, probably non-nucleotide, component in the acid-soluble liver fraction was selectively reduced.) The inhibition of RNA synthesis was associated with a decrease in the RNA polymerase activity of isolated liver nuclei, well established already 45 min after DMNA administration. The reduced activity included both Mg2+- and Mn2+/(NH4)2SO4-stimulated polymerase functions. The inhibition in vivo involved the whole complement of RNA, including poly (A)-containing RNA and isolated poly(A) sequences. The transfer of labelled RNA from the nucleus to the cytoplasm was not impaired. There was no detachment of poly(A)-containing RNA from the microsomes, and the proportion of tightly membrane-bound microsomal RNA and poly(A) sequences was not reduced as determined by use of a flotation technique. No breakage or shortening of the poly(A) chains was indicated by sedimentation analysis.

Nucleosome mono, di, tri-, and tetramers from chicken embryo chromatin

The fractionation of gram quantities of nuclease digested chromatin from chicken embryos into nucleosome mono-, di-, tri-, and tetramers is described in detail. Each of these nucleosomal species contains a fraction soluble in 0-1 M KC1 that decreases with increasing repeat number. Less histone H1 is associated with the nucleosome fractions soluble as compared to the respective fractions precipitated in 0.1 M KC1. Thermal denaturation profiles of the four nucleosomal species are monophasic. The same Tm of 78 degrees C has been determined for the KC1-soluble nucleosomes and for the KC1-insoluble monomer. The Tm of the KC1-insoluble oligomers is 79.8 degrees C. Multiphasic melting curves were recorded for nucleosomal material that was concentrated by lyophilisation or stored at 4 degrees C in 0.25 mM EDTA. Total nucleosome mono-, di-, tri-, and tetramers (consisting of both the fraction soluble and insoluble in 0.1 M KC1) have been analyzed concerning their sedimentation, diffusion, partial specific volume, and molecular weight and compared with the sedimentation and molecular weight data of KC1-soluble nucleosome mono- and tetramers.

Specific inhibition of chromatin-associated poly(A) synthesis in vitro by cordycepin 5′-triphosphate

It has been established that many eukaryotic mRNAs contain poly(adenylic acid) tracts at their 3'-termini. The polyadenylation of mRNA occurs post-transcriptionally in the nucleus as a rapid, initial addition of 100-200 adenylate residues to the pre-mRNA (ref. 1). Subsequently, a slower chain extension (6-8 bases) of the poly(A) tail seems to occur both in the nucleus and in the cytoplasm. The initial polyadenylation reaction can be specifically inhibited by the drug cordycepin (3'-deoxyadenosine) in cell culture, presumably by its conversion to the triphosphate analogue which acts as a competitive inhibitor of poly(A) polymerase. Cordycepin, however, has little effect on the slower poly(A) extension reaction or on the formation of mRNA precursor molecules; but it can inhibit rRNA synthesis. Contrary to the in vitro observations, cordycepin 5'-triphosphate (3'dATP) is not a specific inhibitor of poly(A) synthesis in vivo, relative to RNA synthesis, and RNA polymerase I (which synthesises rRNA) is actually less sensitive to inhibition by 3'dATP than RNA polymerase II (ref. 10) (which is presumed to be involved in the synthesis of mRNA). Since nuclear poly(A) polymerase occurs in two functional states as 'free' and 'chromatin-bound' forms, we reasoned that if the chromatin-associated poly(A) polymerase were involved in the initial polyadenylation of mRNA, it might be selectively inhibited by 3'dATP. The present studies, designed to test such an idea, demonstrate that, as in vivo, the initial polyadenylation reaction can be selectively inhibited in vitro by low levels of 3'dATP. These data also show that higher levels of 3'dATP can inhibit RNA synthesis, 'chromatin-bound' RNA polymerase I activity being significantly more sensitive than the 'bound' RNA polymerase II activity.

Daunorubicin inhibition of DNA-dependent RNA polymerases from Ehrlich ascites tumor cells

Two different forms of DNA-dependent RNA polymerase have been solubilized and purified from nuclei of Ehrlich ascites tumor cells. The purification procedure involves ammonium sulfate precipitation and gel filtration on Sephadex G-25. The separation of A and B activities is achieved by chromatography on DEAE-cellulose. Nuclei are prepared from cells, sensitive or resistant to daunorubicin. RNA polymerases A and B have an absolute requirement of divalent cations for activity. Native DNAs are better templates than heat-denatured DNAs for RNA polymerase A. On the contrary heat-denatured DNA is more transcribed than the native one by RNA polymerase B. The low level of transcription of total and nucleolar ascites DNAs is due to the DNA, the same results being obtained with ascites and calf thymus RNA polymerases A and B. The inhibitory action of daunorubicin on RNA polymerases A and B from Ehrlich ascites tumor cells has been studied in vitro. The same results are obtained with enzymes extracted from sensitive or resistant cells. Daunorubicin does not inhibit the binding of RNA polymerases to the DNA template, but prevents the transformation of the DNA-daunorubicin-RNA-polymerase unstable complex into the highly stable one. This inactive ternary complex has a dissociation rate faster than the stable complex formed without daunorubicin. The size of the RNA synthesized in the presence or absence of daunorubicin is the same.