Quantitation of ovalbumin mRNA in hen and chick oviduct by hybridization to complementary DNA. Accumulation of specific mRNA in response to estradiol

Guinea-pig milk-protein synthesis. Isolation and characterization of messenger ribonucleic acids from lactating mammary gland and identification of caseins and pre-alpha-lactalbumin as translation products in heterologous cell-free systems

1. The major milk proteins synthesized by the lactating mammary gland of the guinea pig were identified and designated as caseins A, B and C and alpha-lactalbumin, with estimated mol.wts. of 28000, 25500, 20500 and 14500 respectively. 2. Antisera to the total casein fraction and to alpha-lactalbumin were prepared from rabbits. The milk proteins were also iodinated with either 131I or 125I. 3. A poly(A)-rich RNA fraction was isolated from lactating guinea-pig mammary glands. Isolation was by affinity chromatography on oligo(dT)-cellulose. 4. Examination of this RNA fraction by electrophoresis on polyacrylamide gels containing formamide indicated three major species 1, 2 and 3, with estimated wol.wts. of 5.4 X 10(5) and 3.3 X 10(5), and the apparent absence of rRNA species. 5. The poly(A)-rich RNA stimulated protein synthesis in heterologous cell-free systems based on wheat germ, Krebs II ascites-tumour cells, and the latter supplemented with an initiation factor-3 fraction from rabbit reticulocyte ribosomes. 6. Between 80 and 90% of the protein synthesis directed by the mRNA was for milk proteins. 7. Analysis of the proteins immunoprecipitated by the alpha-lactalbumin antiserum showed in the wheat-germ system that the product was a protein with a molecular weight greater than that of alpha-lactalbumin, whereas in the ascites-tumour-cell systems both this protein and alpha-lactalbumin were found. When the larger protein was treated with CNBr and the resulting peptides were examined, it was shown that the extra peptide was at the N-terminus. This and other evidence is adduced for the initial translation product of alpha-lactalbumin being a precursor with an addition of about ten amino acids at the N-terminus. 8. Similar analysis of the casein immlnospecific proteins produced under the direction of mRNA indicated that the products had a molecular weight that was apparently a littel smaller than that of the caseins synthesized in vivo. This was not consistent with higher-molecular weight casein precursors. 9. Possible explanations for the results obtained are discussed, especially in terms of the physiological significance of the pre-alpha-lactalbumin as a secretory protein.

A significant lag in the induction of ovalbumin messenger RNA by steroid hormones: a receptor translocation hypothesis

Although ovalbumin and conalbumin mRNA accumulate in the same tubular gland cells of the chick oviduct in response to estrogen or progesterone treatment, the kinetics of induction are markedly different. Conalbumin mRNA begins to accumulate within 30 min after estrogen administration, whereas there is a lag of approximately 3 hr before ovalbumin mRNA begins to accumulate, as measured by three independent assays. The kinetics of estrogen-receptor binding to chromatin indicate that these sites are saturated within 15 min of estrogen administration to the chicks, demonstrating that the lag is not due to slow uptake of the steroid. Suboptimal doses of estrogen produce the same lag, but the resultant rate of ovalbumin mRNA accumulation is lower than with an optimal dose. Partial induction of ovalbumin mRNA by a low dose of estrogen does not shorten the lag with an optimal dose. With progesteone, there is a lag of about 2 hr before either ovalbumin or conalbumin mRNA begins to accumulate. Treatment of chicks with hydroxyurea shortens the lag for ovalbumin induction with either hormone. Inhibition of protein synthesis with emetine does not prevent the accumulation of either ovalbumin or conalbumin mRNA. With cycloheximide, however, ovalbumin mRNA accumulation can be prevented. The existence of a lag suggests that there are intermediate steps between the binding of steroid receptors to chromatin and the induction of ovalbumin mRNA. There are basically two models to explain these delays in response: one involving the accumulation of an essential intermediate, and the other involving a rate-limiting translocation of steroid receptors from initial nonproductive chromatin-binding sites to productive sites. Several aspects of the kinetics of ovalbumin mRNA induction are more consistent with the latter model.

Induction of globin mRNA accumulation by hemin in cultured erythroleukemic cells

The role of heme in erythroid development is investigated in erythroleukemic (Friend) cells. Exogenous hemin induces the accumulation of globin mRNA and globin protein in T3-C12 erythroleukemia cells to levels comparable to those induced by polar solvents, such as dimethylsulfoxide (DMSO). The hemin concentration required for maximal induction (10(-4) M) is the same as that which stimulates globin message translation in reticulocytes or cell-free reticulocyte lysates. Hemin and DMSO together cause T3-C12 cells to accumulate 8-9 fold more globin mRNA than either inducer individually. The kinetics of globin mRNA induction in hemin as compared to DMSO are very different: globin message accumulation begins 4 hr after hemin addition, but not until 30--40 hr after DMSO addition. Biliverdin induces 20--40 fold less hemoglobin than hemin; delta-aminolevulinic acid and porphobilinogen do not induce.

Effects of estrogen and progesterone on transcription, chromatin and ovalbumin gene expression in the chick oviduct

The effects of estrogen, progesterone and estrogen + progesterone combined on nuclear transcriptional processes in oviducts of immature chicks, previously withdrawn from estrogen, are reported. The responses to the steroids of the endogenous nuclear RNA polymerase activities, both nucleolar (I) and nucleoplasmic (II), the chromatin compositions and template capacities, and the appearance of ovalbumin messenger RNA (mRNA) are compared. When immature chicks (previously treated at 14 days with estrogen) are withdrawn from estrogen treatment, there is a gradual reduction in both polymerase activities. Diurnal variations in polymerase II activties in the oviduct of withdrawn chicks required that subsequent experiments include time-matched controls. The hormones alter RNA polymerase II and II activities in vivo as assayed in isolated nuclei. Progesterone represses the polymerase I and II activities, while estrogen alone and estrogen + progesterone enhance both polymerase activities immediately after injection. Diethylstillbestrol, a synthetic estrogen, causes changes similar to those of estrogen. The effects of these steroids on the polymerases are detected within 15 min of hormone injection. Changes in the capacities of chromatins to serve as template for RNA synthesis in general correlated with changes in polymerase II activities. Interestingly, in the case of estrogen treatment, the acidic chromatin protein (but not histone) levels fluctuate positively with the template capacities of the chromatin. An antagonism between estrogen and progesterone is observed in the responses of both RNA polymerases I and II activities as well as in the chromatin template capacity. Levels of messenger RNA coding for ovalbumin, as detected by hybridization with labeled complementary DNA, increase in oviducts of withdrawn chicks within 2--3 of the injection of estrogen, progesterone or estrogen + progesterone. This rapid accumulation of ovalbumin mRNA is not accompanied in each case by a similar increase in polymerase II activity or chromatin template capacity.

The translational capacity of deadenylated ovalbumin messenger RNA

We present evidence that the poly(A) sequence at the 3' end of ovalbumin mRNA has an effect on its translational efficiency in a reticulocyte lysate cell-free system. Polynucleotide phosphorylase has been used to remove selectively the poly(A) while leaving the rest of the molecule intact. It is shown that the stability of the mRNA in a cell free system is not appreciably affected by this procedure. Measurements of the size of ovalbumin-synthesizing polysomes, rate of peptide elongation, and number of rounds of translation per messenger show a generally reduced efficiency for deadenylated mRNA compared to native mRNA. No comparable difference was observed in experiments with a wheat germ cell-free system, which gives few rounds of translation per mRNA. This indicates that the effect results from a lowering of the efficiency of reinitiation on deadenylated mRNA.

Quantitation of elongating form A and B RNA polymerases in chick oviduct nuclei and effects of estradiol

The number of elongating form A and B RNA polymerases in chick oviduct nuclei was estimated by measuring incorportaion of 3H-UTP into 3' termini of nascent RNA chains in the presence of heparin to inhibit initiation, and quantitation labeled uridine released from these termini after alkaline hydrolysis. The method corrects for conversion of UMP to uridine (U) during manipulations and for production of 3' termini by ribonucleases and phosphatases. The results indicate that a large fraction of RNA polymerases elongating in vivo is retained in isolated nuclei: per diploid genome, approximately 1 x104 form B and 2 x103 form A enzymes are present. These levels are sufficient to maintain normal in vivo rates of mRNA and rRNA synthesis, but the average density of packing of polymerases on DNA is considerably less than the maximum density predicted by Miller and Bakken (1972), suggesting that initiation of polymerases of DNA is a limiting factor in the control of transcription. Rates of elongation of polymerases in vitro are severely impaired, indicative of a loss of elongation factors during nuclear isolation. After 6 hr of estradiol treatment in vivo, the level of form A enzymes in ovoduct nuclei increases to 5 x 103; little change in the number of form B enzymes is seen.

Differential subnuclear distribution of polyadenylate-rich ribonuclei acid during induction of egg-yolk protein synthesis in male Xenopus liver by oestradiol-17 beta

A 4-8-fold increase in the rate of hepatic nuclear RNA synthesis occurred within 11 h after a single injection of oestradiol-17 beta to male Xenopus to induce egg-yolk protein synthesis. 2. By using a gentle procedure for fractionating nuclei into their major structurally different components [J. R. Tata& B. Baker (1974) Exp. Cell Res. 83. 111-124], it was found that the hormone-induced increase in the total amount of newly made RNA was associated with a 2-10-fold increase in the poly(A) content of nuclear RNA. 3. When the poly (A) content of nuclear RNA was determined by hybridization to poly[3H](U) or specific binding to oligo(dT)-cellulose, most of the increase (10-fold) in poly (A) content of newly synthesized RNA was associated with the euchromatin fractions, whereas the increase was less marked in the other subnuclear fractions. 4. Resolution of nuclear RNA into poly (A)-poor and poly(A)-rich RNA species by chromatography on oligo(dT)-cellulose, followed by polyacrylamide-gel electrophoresis with sodium dodecyl sulphate or in the pressence of 99% formamide, revealed that the hormone caused a preferential enhancement of high-molecular-weight (25S-60S) poly (A)-rich HnRNA (heterogeneous nuclear RNA,) much of which was associated with euchromatin and not with the nuclear sap. 5. Induction of vitellogenin in male frogs was in particular characterized by the appearance of a high-molecular-weight polyadenylated component exhibiting a peak at 35-36S, i.e. a molecular weight of approx. 2.05x10(6)+/-0.15x10(6). Although there is no evidence as yet that such a polyadenylated high-molecular-weight nuclear RNA species contains sequences corresponding to vitellogenin mRNA, it is possible that a high proportion of the most stable form of the putative nuclear precursor to vitellogenin mRNA induced by oestrogen in male Xenopus liver may be only marginally bigger than the cytoplasmic mRNA, and may at any one time be predominantly associated with the euchromatin fraction.

Full length and discrete partial reverse transcripts of globin and chorion mRNAs

Rabbit globin mRNA was copied by AMV reverse transcriptase in the presence of various concentrations of deoxyribonucleotides (dNTPs). The cDNAs were analyzed by electrophoresis under denaturing conditions in formamide-polyacrylamide gels. Discrete size products were detected, ranging from 65 to 650 nucleotides-that is, up to the full length of the mRNA template. Increasing the concentrations of all four dNTPs stimulated formation of full-length transcripts and made the incomplete copies less abundant. Hybridization and nuclease digestion experiments indicated that the full-size product is indeed a complete transcript of globin mRNA. Similar results were obtained with chorion mRNAs. The possible usefulness of the discrete partial transcripts is discussed.