Hybridization of ribosomal RNA labeled to high specific radioactivity with dimethyl sulfate

Constancy of ribosomal RNA genes during aging of mouse heart cells and during serial passage of WI-38 cells

The DNA content and ribosomal RNA gene copy number in heart of the inbred mouse strain C57BL/6 were determined at different ages. The DNA content of mouse heart remained constant, at about 150 micrograms DNA per heart, from 1 to 30 mth of age. The number of rRNA genes, as estimated by 28S rRNA . DNA hybridization, was not found to change significantly as a function of age. Likewise, the extent of rRNA hybridization to DNA from cultured human WI-38 cells at early and late passage levels was the same. These data support the notion that genomic rDNA sequences are not lost during in vivo and in vitro aging. However, the rDNA sequences are quite large and numerous small deletions or base pair substitutions would not have been detected in these studies.

Isolation of nucleolar DNA-binding proteins by simultaneous, competitive DNA--sephadex affinity chromatography

A new method is described for the isolation of sequence-specific DNA-binding proteins, based on simultaneous, competitive binding to homologous or heterologous DNA. Since both types of DNA are bound to a solid matrix (Sephadex beads), the method may be used for the preparative isolation of proteins which bind preferentially to specific DNA sequences. Fractionation of nucleolar proteins from Novikoff hepatoma ascites cells by this technique yields two protein fractions which show much greater apparent specificity of binding to homologus DNA, in a nitrocellulose filter-binding assay, than unfractionated nucleolar proteins.

Hybridization properties of human X-chromosomal RNA transcripts from murine--human hybrids

A human--mouse hybrid cell line which has retained the human X chromosome and a fragment of chromosome 2 contains RNA sequences transcribed from human DNA. Nuclear RNA enriched for human sequences was prepared from this hybrid cell line by a multistep hybridization procedure to mouse and human DNA immoblized on nitrocellulose filters. The properties of this RNA were analyzed by RNA--DNA hybridization techniques. The results indicate that we have prepared a RNA fraction enriched for sequences homologous to repeated DNA sequences of the human X chromosome.

Organization and transcriptional activity of brain chromatin subunits

Digestion of brain nuclei with micrococcal nuclease produces 11.2-S chromatin subunits which comprise up to 80% of the total nuclear DNA. Hybridization studies with excess subunit DNA demonstrate that subunits are distributed throughout the repeated and nonrepeated sequences of the genome. No class of nonrepeated DNA appears to be excluded from subunits. Transcribed DNA is present in chromatin subunits since in vitro labelled poly(A+)-mRNA hybridizes to excess subunit DNA with kinetics identical to that for total DNA.

Analysis of rabbit brain polysomal poly (A+) mRNA by DNA excess hybridization

DNA sequence representation in rabbit brain mRNA was examined by DNA excess hybridization. purified polysomal poly (A+) mRNA was labeled in vitro with [3H] dimethyl sulfate and reacted at DNA: RNA ratios of 5000 : 1 and 30 000 : 1. Poly(A+) mRNA hybridizied mainly to nonrepeated DNA with a smaller kinetic component which was complementary to repeated DNA sequences. The latter component was not due to nuclear or ribosomal RNA contamination. Poly(A-) RNA purified from brain polysomes hybridized to excess DNA as a single repeated component. Thermal denaturation profiles of the RNA - DNA hybrids indicated a high degree of fidelity in base pairing.

A new estimate of human ribosomal gene number

Radioactively labelled DNAs (5 X 10(6) cpm/mug) complementary to human 18 S and 28 S ribosomal RNA were synthesized using RNA-directed DNA polymerase (EC 2.7.7.7). These complementary DNAs were used to measure human ribosomal gene numbers by two independent methods, both of which indicated numbers at least four-fold lower than those previously reported. First, the kinetics of the annealing of the complementary DNAs with total human placental DNA indicated that the number of both 18-S and 28-S ribosomal genes per haploid genome is approximately 50. Second, saturation experiments in which a constant amount of DNA was annealed with increasing amounts of complementary DNA also indicated that the number of 28 S ribosomal RNA genes in human placental and spleen DNA is is about 50 per haploid genome.

Characteristics of ribonucleic acids isolated for Botryodiplodia theobromae pycnidiospores

Nucleic acids isolated for dormant and germinated Botryodiplodia theobromae pycnidiospores contain five distinct species of RNA. They include two ribosomal species, two "ribosomal-associated" species and transfer RNAs. Sedimentation coefficients of 25.1S and 18S were obtained for the two ribosomal RNA species and 5.8S and 5S for the two "ribosomal-associated" RNA components. Molecular weights of 1.20,0.67,0.054 and 0.035x106 daltons were obtained after formaldehyde treatment and electrophoresis on polyacrylamide gels for these same four RNAs. Methylated nucleotides were present in the transfer RNAs and large and small ribosomal RNAs; in contrast 5.8S and 5S RNAs contained few methylated nucleotides. In addition to the 5 distinct RNA species, polyadenylate-containing RNA was isolated from both dormant and germinated spores.

Messenger ribonucleic acid metabolism in mammalian mitochondria. Discrete poly(adenylic acid) lacking messenger ribonucleic acid species associated with mitochondrial polysomes

The mRNA species released from mitochondrial polysomes prepared by the Mg2+ precipitation technique have been further characterized using various analytical techniques. Mitochondrial polysomes were dissociated by treatment with puromycin and chemically labeled with (3H) dimethyl sulfate. About 51% of steady-state mitochondrial mRNA bind to oligo(dT)-cellulose indicating the presence of poly(adenylic acid)(poly(A)) in this fraction. The poly(A)-containing mRNAs resolve into discrete bands of 9-16 Se, while the RNA fraction unable to bind to oligo(dT)-cellulose representing poly(A)-lacking mRNA contains 8-12 Se species. About 90% of poly(A) lacking RNA hybridizes with mitochondrial DNA and less than 7% hybridizes with nuclear DNA. The extent of hybridization of poly(A)-lacking RNA with mitochondrial DNA was not significantly affected by the presence of excess mitochondrial rRNA, cytoplasmic rRNA, or a tenfold concentration of poly(A)-containing RNA isolated from total mitochondrial RNA. Possible differences in sequence properties between poly(A)-containing and -lacking mitochondrial mRNAs were further verified using a solid phase-bound cDNA procedure. Poly(A)-containing mRNA released from mitochondrial polysomes shows over 85% sequance homology with oligo(dT)-cellulose-bound cDNA prepared against total mitochondrial poly(A)-lacking mitochondrial mRNA hybridizes with the cDNA providing direct evidence for the distinct sequence properties of the two mRNA species.

Ribosomal RNA gene dosage as a function of tissue and age for mouse and human

The average number of rRNA genes per haploid genome (rRNA gene dosage) of the cells present in liver and brain was determined throughout the lifespan of the inbred C57BL/6J mouse strain and of human. Ribosomal RNA gene dosage was determined using the RNA-excess DNA - RNA hybridization technique. DNA was extracted and purified using a CsCl/chloroform method with a high percent yield (over 90%) to minimize any possible effects of tissue and age-dependent selective loss or gain of rRNA genes. Radioactive rRNA was from the liver of the youngest age group for either mouse or human in all hybridization experiments, with DNA from the different tissues and age groups being the only variable. In the young mouse (35-49 days), the rRNA gene dosage was 36% higher in brain (114 genes), as compared to liver (84 genes). The rRNA gene dosage remained essentially constant as a function of age for mouse brain; but between the age of about 220 to 440 days, it increased in liver, attaining approximately an equal value to that of brain. No significant difference was found in the rRNA gene dosage of brain or liver between different mice of the same age. In contrast to this result, a significant difference was found between human tissues of similar age. The rRNA gene dosage ranged about 2-fold (148-289) between 2 months to 75 years of age. An age-dependent trend, similar to that for mouse liver, was found when the averages of four different age groups totaling 20 individuals were compared. However, this was not statistically significant. No difference in the rRNA gene dosage as a function of sex or tissue was apparent. Several models are discussed to account for these results.