Animal DNA-dependent RNA polymerases. 1. Large-scale solubilization and separation of A and B calf-thymus RNA-polymerase activities

Mechanism of action of antimycobacterial activity of the new benzoxazinorifamycin KRM-1648

The mechanism of antimicrobial activity of KRM-1648 (KRM), a new rifamycin derivative with potent antimycobacterial activity, was studied. Both KRM and rifampin (RMP) inhibited RNA polymerases from Escherichia coli and Mycobacterium avium at low concentrations: the 50% inhibitory concentrations (IC50s) of KRM and RMP for E. coli RNA polymerase were 0.13 and 0.10 micrograms/ml, respectively, while the IC50s for M. avium RNA polymerase were 0.20 and 0.07 microgram/ml. Both KRM and RMP exerted weak inhibitory activity against Mycobacterium fortuitum RNA polymerase, rabbit thymus RNA polymerases, E. coli DNA polymerase I, and two types of reverse transcriptases. Uptake of 14C-KRM by M. avium reached 18,000 dpm/mg (dry weight) 1.5 h after incubation, while uptake by E. coli cells was slight. KRM was much more effective in inhibiting uptake of 14C-uracil than was RMP (IC50 of KRM, 0.04 microgram/ml; IC50 of RMP, 0.12 microgram/ml). These findings suggest, first, that the potent antimycobacterial activity of KRM is due to inhibition of bacterial RNA polymerase and, second, that the activity of KRM against target organisms depends on target cell wall permeability.

A beta-turn in alpha-amanitin is the most important structural feature for binding to RNA polymerase II and three monoclonal antibodies

Four amatoxin-binding proteins with KD values in the nanomolar range, 3 monoclonal antibodies and RNA polymerase II, were studied with respect to their affinities to 24 alpha-amanitin derivatives with modified side chains. From KD values we estimated the amounts of binding energy that single side chains of the amatoxins contribute to complex formation. Ile6, previously identified by X-ray analysis to be part of a beta-turn (Kostansek EC, Lipscomb WN, Yocum RR, Thiessen WE, 1978, Biochemistry 17:3790-3795) proved to be of outstanding importance in all complexes. Replacement of the isoleucine with alanine reduced the affinity to all binding proteins to < 1%, suggesting a strong hydrophobic interaction. A strong effect was also seen when Gly5 was replaced with alanine, suggesting that the absence of a side chain in proximity to the beta-turn is likewise important. In addition to the beta-turn, each of the proteins showed at least 2 other points of strong contact formed by hydrogen bonds. Donors are the indole NH of 6'-hydroxy-Trp4 and OH of hydroxy-Pro2 and dihydroxy-Ile3. All the antibodies, but not RNA polymerase II, recognized the indole nucleus of 6'-hydroxy-Trp4. The geometric arrangement of the 4 strongest contact points suggests that the amatoxin binding site is different in each of the 4 proteins, except for the 2 antibodies raised in the same animal. Here, most of the contact points were identical but differed in strength of interaction. The method of structural analysis presented in this study is useful for identifying contact sites in complexes of proteins with peptides of rigid conformation. Furthermore, the method complements X-ray data by providing information on the amount of binding energy contributed by single structural elements.

Purification of a cytosolic factor from rat liver that stimulates transcription in isolated nuclei and its action on purified RNA polymerase II-DNA system

A cytosolic factor that stimulates transcription in isolated nuclei was purified approximately 4000-fold to near homogeneity from rat liver. The molecular weight of the factor was determined as 47 000 by SDS-polyacrylamide gel electrophoresis. The factor had no detectable deoxyribonuclease and protease activity but showed ribonuclease inhibitor activity. The factor could stimulate transcription in isolated nuclei by 50% at about 3.0 ng and the maximal stimulation was about 100%. When [gamma-S]ATP and [gamma-S]GTP were included in the reaction, the factor stimulated the synthesis of RNA which was able to bind to a mercury-Sepharose column and about 80% of the bound RNA was sensitive to a low concentration of alpha-amanitin. When heparin was added before initiation to preincubation mixture containing RNA polymerases II and DNA, a small but definite incorporation of [14C]UTP was observed. The factor alone had no stimulatory effect on the heparin-resistant incorporation of [14C]UTP but, in the presence of two rat liver nuclear fractions, phosphocellulose 0.5 and 1 M KCl step fractions, could stimulate the incorporation above the level with the combination of the two nuclear fractions. Antibody raised against the factor inhibited accurate transcription from the adenovirus 2 major late promoter in a nuclear lysate from Ehrlich ascites tumor cells, and the inhibition was neutralized by the factor.

Isolation of herpes simplex virus regulatory protein ICP4 as a homodimeric complex

The viral polypeptide ICP4 (or Vmw175) is synthesized during the immediate early phase of infection by herpes simplex virus and regulates the transcription of delayed early and late viral genes. We obtained a partially purified preparation of soluble ICP4 under nondenaturing conditions. Physical constants for native ICP4 were empirically determined by molecular sieve chromatography and sucrose density gradient ultracentrifugation. The Stokes radius of native ICP4 was 8.72 X 10(-7) cm. The sedimentation coefficient of native ICP4 was 9.00S. From these values, the calculated molecular weight of native ICP4 was 342,000, a value which is twice that of monomeric ICP4, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The failure of any other polypeptides to specifically coprecipitate with native ICP4 in the presence of anti-ICP4 antibody indicates that the 342,000-dalton complex is a homodimer of ICP4. The frictional coefficient ratio of native ICP4, which is 1.9, indicates that the homodimer is a highly elongated molecule.

Is actin a transcription initiation factor for RNA polymerase B?

We have previously reported that two fractions derived from HeLa cell S100 extracts, the heparin flow-through and the heparin 0.6 M KCl eluate are required in vitro for efficient and accurate transcription by RNA polymerase class B (II). We have further purified a factor present in the heparin flow-through fraction, which markedly stimulates specific transcription catalyzed by the heparin 0.6 M KCl eluate. We report here that some of the properties of the stimulatory factor present in our most purified fractions are strikingly similar to those of actin. We demonstrate also that this factor acts at the pre-initiation level of the transcription reaction.

High salt effect on RNA synthesis in Krebs ascites tumor cells

The incubation of Krebs ascites tumor cells in medium with a high salt concentration resulted in a partial inhibition of nuclear RNA synthesis. The residual RNA polymerase activity in such nuclei was only slightly inhibited by low concentrations (50 nM) of alpha-amanitin. This finding suggested an inhibition of RNA polymerase II activity under conditions of medium hypertonicity. Indeed, RNA polymerase II, isolated from the nuclei of cells exposed to hypertonicity, revealed only half of the control activity. On the other hand, RNA polymerase I was not affected by hypertonicity. Moreover, chromatin fractions isolated from cells incubated in hypertonic or isotonic medium were equally template-active in RNA synthesis.

Immunological relatedness of subunits of RNA polymerase II from insects and mammals

A procedure is described which allows rapid purification of RNA polymerase II from either embryos of Drosophila melanogaster or larvae of Chironomus thummi. The polypeptide compositions of the enzymes were compared in denaturing gels. Antisera were raised against the native enzymes and were tested for binding activity to separated subunits of each enzyme. Sheep antibodies to Drosophila RNA polymerase were found to react with most polypeptides of the insect RNA polymerases but only with the high-molecular weight subunits of calf thymus RNA polymerase II. These were also found to cross-react with a monoclonal antibody directed against the large subunits of the Drosophila enzyme. An antiserum to Chironomus RNA polymerase II reacted with the three largest subunits of this enzyme and subunits 0, 1 and 2 of Drosophila RNA polymerase II. The purified IgG fractions of the polyspecific antisera inhibited the activity in vitro of the insect RNA polymerases to different degrees.

RNA polymerase III from Drosophila hydei pupae. Purification and partial characterization

DNA-dependent RNA polymerase III, which is usually highly resistant to alpha-amanitin, has been purified from Drosophila hydei pupae. The enzyme is insensitive to alpha-amanitin concentrations up to 0.1 microM; at 100 microM alpha-amanitin the enzyme activity is inhibited by approximately 10%. The enzyme was extracted at low ionic strength and purified to homogeneity by six purification steps; 0.1--0.2 mg enzyme/kg pupae could be obtained. The subunit composition of the enzyme was determined after sucrose-gradient centrifugation by sodium dodecyl sulphate electrophoresis in polyacrylamide gels. The enzyme was resolved into putative subunits of molecular weight 154 000, 135 000, 62 000, 58 000, 38 000, 32 000, 31 000, 27 200, 26 500, 21 500 and 17 500. This subunit composition is in general accord with that of eucaryotic class III enzymes. The catalytic properties (salt-activation profile, ratio of activity with denatured DNA to that with native DNA) and the order of elution of the enzyme from DEAE-cellulose with respect to RNA polymerase II agree with the classification of the isolated enzyme as an RAN polymerase III.

The effect of pyrophosphate analogues on influenza virus RNA polymerase and influenza virus multiplication

Analogues of pyrophosphate have been tested as inhibitors of influenza virus-RNA polymerase activity in cell-free assays. The most active compound, phosphonoformic acid (PFA), reduced the polymerase activity to 50 per cent at a concentration of 20 muM. The inhibition was dependent on the type of divalent cation present in the assay. PFA at a concentration of 400 muM also inhibited the influenza virus plaque formation by 90 per cent.

Transcription by eukaryotic RNA polymerases A and B of chromatin assembled in vitro

Chromatin was assembled in vitro from simian virus 40 DNA form I and the calf-thymus four histones H2A, H2B, H3 and H4. Transcription with calf thymus RNA polymerases A and B (I and II) was greatly inhibited. Nucleosomes were found to inhibit both RNA chain initiation and elongation. The inhibition of elongation could be relieved by increasing ionic strength, suggesting that electrostatic interactions between histone octamer and DNA have to be broken for RNA polymerase to transcribe DNA organised into nucleosomes.

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).

Transcription in vitro of adenovirus-2 DNA by RNA polymerases class C purified from uninfected and adenovirus-infected HeLa cells

DNA-dependent RNA polymerase class C (or III) has been solubilized from either uninfected or adenovirus-2-infected HeLa cells and purified by chromatography on phosphocellulose, DNA-cellulose, CM-Sephadex and DEAE-Sephadex. The last column separated the enzyme into three forms CI, CII and CIII, which were completely free of RNA polymerases class A and B and of DNase and RNase. The total and the relative amount of these different enzyme C forms did not vary whether purified from uninfected or infected cells. Irrespective of the stage of purification, the three enzyme forms transcribed deproteinized adenovirus-2DNA very efficiently. This transcription was highly sensitive to elevated ionic strength (especially in the presence of Mg2+) and was accompanied by continuous reinitiation as shown by adding poly(rI), a potent inhibitor of initiation. In addition heparin-resistant initiation complexes could be formed at elevated temperature. The RNA synthesized in vitro on deproteinized intact adenovirus-2 DNA by the different forms of RNA polymerase class C, has been characterized. Analysis of the transcripts by gel electrophoresis, RNA self-annealing, hybridization to separated adenovirus-2 DNA strands and to restriction endonuclease (BamHI, HindIII), adenovirus-2 DNA fragments have demonstrated that restriction endonuclease (BamHI, HindIII), adenovirus-2 DNA fragments have demonstrated that the various regions of the adenovirus-2 genome were randomly transcribed. In addition, hybridization of RNA transcripts labelled at their 5' end by either [gamma32P]ATP or [gamma-32P]GTP indicated that not only elongation but also initiation occurred randomly through the entire adenovirus-2 genome, irrespective of the form of the enzyme and of the origin of the cells (normal or infected). The results are discussed in terms of the components which are possibly involved in specific transcription.

Evidence for the existence of two forms of RNA polymerases I and II in insect wing epidermis

DNA-dependent RNA polymerases were solubilized from developing wings of the oak silkmoth, Antheraea pernyi, and partially purified by ion-exchange chromatography and sucrose gradient sedimentation. Four enzyme species were resolved on the basis of chromatographic behavior, divalent cation requirements, ionic strength optima, template preference and alpha-amanitin sensitivity. Each class (i.e. RNA polymerase I and II) was present in two forms termed IA, IB and IIA, IIB on the basis of their elution pattern from the column. Both class I enzymes were sensitive to high concentrations of alpha-amanitin but this may be due to general toxicity rather than specific inhibition. The intraclass variants did not differ significantly in enzymatic properties although form IIB was more sensitive to alpha-amanitin (50% inhibition at 2 . 10(-9) M) than form IIA (3 . 10(-8)M).

Characterization of chick liver chromatin and analysis of its in vitro transcription products

Carefully controlled preparation of chromatin from purified chick liver nuclei yielded over 50% native chromatin as shown by the analysis of the nucleosome pattern after micrococcal nuclease digestion. The size of DNA in this chromatin as analyzed on alkaline sucrose gradients varied from 10S to 19S, the majority being 14S. All endogenous RNA polymerases were represented in the chromatin preparation although to different extents: RNA polymerase I was the most and RNA polymerase II the least abundant. Initiation studies showed that endogenous RNA polymerase II was capable of initiating RNA chains during 5 min. Saturation of chromatin with purified homologous RNA polymerase II increased initiation to 10 min. The addition of heparin caused the RNA transcribed to be larger in size and of increased yield. Chromatin transcription with added purified RNA polymerase II in the presence of heparin produced RNA as large as 32S. A chromatin preparation of this kind would therefore be suitable to transcribe any eukaryotic gene invitro provided additional homologous RNA polymerase II is used.Images

Enzymatic properties of viral replication complexes isolated from adenovirus type 2-infected HeLa cell nuclei

When HeLa cell nuclei, isolated 17 h after infection with adenovirus type 2 (Ad2), were extracted with 200 mM ammonium sulfate, Ad2 nucleoprotein complexes were selectively released. These complexes contained a DNA polymerase activity that corresponded to DNA polymerase molecules actively engaged in Ad2 DNA replication. Under our high-salt (200 mM ammonium sulfate) incubation conditions, where no reinitiation occurred, full-length Ad2 DNA chains were synthesized by elongation of chains that had been initiated in vivo. This conclusion was further supported by density labeling experiments indicating that the in vitro DNA synthesis was semiconservative. Evidence is presented suggesting that at least part of the DNA polymerase molecules engaged in Ad2 DNA replication belong to the gamma class.

Initiation and elongation of polyribonucleotide chains on rat ventral-prostate chromatin transcribed by homologous ribonucleic acid polymerase B

The characteristics of initiation of RNA synthesis and the elongation of RNA chains on rat ventral-prostate chromatin by RNA polymerase B were investigated by two methods. 1. Initiation was carried out under low-salt conditions with three ribonucleoside triphosphates, and elongation was begun in the absence of reinitiation by the addition of the fourth ribonucleoside triphosphate and increasing the salt concentration. 2. Stable initiation complexes were formed by preincubation of enzyme with template at 37 degrees C, elongation was started by the addition of all four ribonucleoside triphosphates and reinitiation or spurious RNA synthesis was prevented by rifamycin AF/013. The latter method gave more reliable results. The dependence of those parameters on the androgenic status of the animal was studied. During the first 24h after castration, elongation was mainly affected, whereas after 72h a smaller number of initiation sites for RNA polymerase B on chromatin was evident. Considerable diurnal variations in the various parameters were observed. Changes in the relative concentrations of the chromatin-associated proteins were also observed after castration. In the rat ventral-prostate gland androgenic steroids may not only influence one stage of the transcriptional process, but may affect many factors involved in the control of gene expression.

Inhibition of influenza virus ribonucleic acid polymerase by ribavirin triphosphate

Ribavirin 5'-triphosphate (RTP), derived from the broad-spectrum antiviral compound ribavirin (Virazole), can selectively inhibit influenza virus ribonucleic acid polymerase in a cell-free assay. Ribavirin and its 5'-monophosphate have no effect on the polymerase. The inhibition is competitive with respect to adenosine 5'-triphosphate and guanosine 5'-triphosphate. RTP also inhibits ApG- and GpC-stimulated influenza virus ribonucleic acid polymerase. Since ribavirin is phosphorylated in the cell, the inhibition of influenza multiplication in the cell may also be caused by RTP.

Multiple forms of DNA-dependent RNA polymerase I from immature chick liver. Selective effect of 17beta-estradiol

1. We found that a single injection of 17beta-estradiol into immature chicks resulted within 24 h in a 2-fold increase of the transcripitional capacity of liver nuclei which involved both endogenous RNA polymerase I and II actvities. Similarly, RNA polymerase activity I of purified nucleoli was also doubled. 2. During purification of RNA polymerase I from controls and treated chicks the difference in activity was almost completely lost. 3. RNA polymerase I could be resolved into two forms, IA and IB, on CM-Spehadex. Form IA increased and form IB decreased after estrogen treatment while the sum of the two remained constant. Form IA sedimented more slowly than form IB in glycerol gradients and was predominant in purified nucleoli. 4. These observations suggest that there may be an equilibrium between the two forms of RNA polymerase I which may change in order to produce the translational shift-up which occurs after estrogen treatment.

Stimulation of RNA polymerase I and II activities by 17 beta -estradiol receptor on chick liver chromatin

The endogenous transcriptional capacity (RNA polymerase I and II activity) of liver chromatin from chicks treated with 17 beta-estradiol for 24 h (E 24) was double that of the controls. E 24 chromatin contained estradiol receptor activity while control chromatin did not. Its presence suggested an implication in the enhanced activities of RNA polymerases of E 24 chromatin. When semi-purified estradiol receptor was added to control chromatin, the endogenous transcriptional capacity of this chromatin was greatly increased. Studies with alpha-amanitin showed that both RNA polymerase I and II were stimulated by the estradiol receptor. This stimulation was observed as long as homology of the system was maintained. Solubilized homologous RNA polymerases were stimulated much less by the hormone complex in the presence of heterologous DNA than with homologous chromatin. Prokaryotic RNA polymerase could not be stimulated by chick liver estradiol receptor in the presence of heterologous DNA.

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.

Influence of steroid-receptor complexes on transcription by human hypertrophied prostatic RNA polymerases

The effects of 5alpha-dihydrotestosterone-receptor complexes on transcription in human hypertrophied prostate tissue were studied in a cell-free system reconstituted from the various subcellular fractions prepared from specimens of the diseased gland. Two major RNA polymerase species were isolated from human hypertrophied prostate. These were designated A and B and were distinguishable by their preference for divalent cations and their sensitivity to salt and alpha-amanitin. Moreover, RNA polymerase B, but not RNA polymerase A, could effectively transcribe a prostate chromatin template. Any enzyme activity endogenous to some chromatin preparations was shown to be characteristic of RNA polymerase B. 5alpha-Dihydrotestoterone-receptor complexes were transferred into prostatic chromatin both steroid- and tissue-specifically. The association of steroid-receptor complexes with chromatin produced changes in template activity and increased the transcription of the chromatin by exogenous and endogenous RNA polymerase B. With a number of specimens, however, there was considerable variation in accessible cytoplasmic receptor sites, uptake of steroid-receptor complexes by chromatin preparations, the template activity of the chromatin and its response to steroid-receptor stimulation. Nevertheless, the transcription characteristics of human hypertrophied prostatic chromatin appear to be influenced by steroid-receptor complexes, and the extent of the response to added complexes would undoubtedly be governed by pre-existing complexes having had an earlier effect.

Control of RNA synthesis by chromatin proteins

The effect of chromatin proteins on template activity has been studied. Using both E. coli RNA polymerase and calf thymmus polymerase B we have measured the number of initiation sites on chromatin and various histone-DNA complexes. Chromatin can be reconstituted with histone proteins alone and this complex is still a restricted template for RNA synthesis. The removal of histone f1 causes a large increase in the template activity. Chromatin is then treated with Micrococcal nuclease and the DNA fragments protected from nuclease attack ("covered DNA") are isolated. Alternatively, the chromatin is titrated with poly-D-lysine, and by successive treatment with Pronase and nuclease, the DNA regions accessible to polylysine are isolated ("open DNA"). Both fractions were tested for template activity. It was found that RNA polymerase initiation sites are distributed equally in open and covered region DNA.

Characterization of adenovirus type 2 transcriptional complexes isolated from infected HeLa cell nuclei

HeLa cell nuclei, isolated 17 h after infection with human adenovirus type 2 (Ad2), were treated with 200 mM ammonium sulfate. The extract (S200 fraction) contained 50 to 70% of the nonintegrated Ad2 DNA, which was in the form of nucleoprotein complexes. These complexes contained native, intact Ad2 DNA (with the exception of replicative intermediates) and could be partially purified and resolved by velocity gradient centrifugation. Using high-salt (200 mM ammonium sulfate) incubation conditions, more than 95% of the nuclear RNA polymerase activity belonged to class B. About 45% of the class B enzyme molecules bound to DNA in the nuclei (those "engaged" in RNA synthesis) were released from the nuclei in the form of Ad2 transcriptional complexes by treatment with 200 mM ammonium sulfate. At least 90% of the RNA synthesized in high salt in the nuclei or in the S200 fraction was Ad2 specific, and essentially all of this RNA was complementary to the l strand of Ad2 DNA. These findings are compatible with what is known about Ad2-specific RNA synthesis in vivo. The analysis of the RNA synthesized from partially purified transcriptional complexes supports the contention that its transcription is almost entirely asymmetric, and that the asymmetry observed in vivo is not a consequence of the rapid degradation of h-strand transcripts. The RNA synthesized in vitro in the absence of detectable RNase activity sedimented with a maximum size of 35 to 40S. Less than 5% of the nuclear or the S200 fraction RNA polymerase activity was class C when assayed under non-reinitiating conditions. Although much of the RNA synthesized by the class C enzyme was Ad2 specific, 5.5S virus-associated RNA was not the predominant product. The isolation of Ad2 DNA transcriptional complexes provides an attractive system for further characterizing the Ad2 DNA template used for transcription and for studying the regulation of the expression of the Ad2 genome during the productive infection cycle.

Nuclear ribonucleoproteins as inhibitors of mammalian RNA polymerase

A ribonucleoprotein complex isolated from rabbit thymus nuclear lysates was found to be an inhibitor of DNA-dependent RNA polymerase II. The inhibition appeared to be of a competitive type and was completely reversed by high concentration of DNA. Highest inhibition was observed when enzyme and complex were preincubated before addition of DNA while there was little inhibition after enzyme had started synthesis on the DNA template. The RNA isolated from the complex was equally inhibitory and was a more effective inhibitor than either tRNA or rRNA.

Animal DNA-dependent RNA polymerases. Purification and molecular structure of hen-oviduct and liver class-B RNA polymerases

Hen ovidcut and liver class B RNA polymerases have been extensively purified and their molecular structure has been analysed. While only one enzyme B form (BIIb) was found in liver, three forms (BI, BIIa and BIIb) were resolved from oviduct. The molecular structures of the various class B RNA polymerase forms purified from hen oviduct and liver are identical to the corresponding forms previously purified from calf thymus and rat liver. At the present level of resolution the only difference lies in a slight difference in the charge of one subunit (SB2a) of enzyme form BIIa, when comparing the mammal and bird enzymes. It is unlikely that the absence of enzyme forms BI and BIIa in purified hen liver RNA polymerase B could be related to limited and specific proteolysis during the purification, since co-purification of oviduct and liver RNA polymerase B activities from a mixture of oviduct and liver nuclei does not affect the presence of either oviduct enzyme form BI or BIIa in the final purified mixture.

Steroid-induced early protein synthesis in rat uterus and prostate

An early 'induced protein', after exposure of the rat uterus to estradiol, is detected among the soluble proteins with a double-labelling technique and electrophoretic fractionation. Efforts have been directed to establish the subcellular distribution of the induced protein, since such a protein, observable 1 h after hormone administration, may play an important role in the subsequent amplified responses, especially in terms of RNA synthesis. Moreover such an early discrete induced protein was sought in a comparable system responding to another hormone, namely prostate and seminal vesicles under androgens. The induced protein was not found in uterine nuclei of 21-day-old rats after 1 h of estradiol action in vivo and 1 h of tissue incubation with labelled leucine. This negative result summarizes a search among different nuclear protein fractions using various procedures; nor was induced protein observed in mitochondrial and microsomal pellets. Contrary to these negative findings, slight changes of histone labelling were observed under the experimental conditions used to demonstrate induced protein. In addition histone acetylation was increased after 1 h of estradiol action in vivo and 15 min tissue labelling in vitro with radioactive acetate. Furthermore, an increase in total protein synthesis between 0 and 2 h after estradiol action was observed, the relative increase of incorporation of radioactive leucine into protein of estradiol-treated vs non-stimulated uteri being corrected for variations of the acid-soluble radioactive leucine pool. Attempts to obtain an early and discrete induced protein with androgens in prostate and seminal vesicles of immature or castrated rats after different times of exposure to testosterone, androstanolone and estradiol have been unsuccessful. The contribution of both negative and positive findings in steroid-induced early protein synthesis is discussed in the context of the current knowledge of hormone action.