Satellite DNA in constitutive heterochromatin of the guinea pig

Total DNA and DNA from the heterochromatin and euchromatin fractions of male guinea pig liver nuclei were analyzed by cesium sulfate-silver density-gradient centrifugation. Total DNA is composed of three components: a heavy satellite DNA, a main DNA of intermediate density, and a light satellite DNA. Heterochromatin DNA shows a fourfold enrichment in the satellite components while euchromatin DNA is relatively devoid of them. The strands of both satellite DNA's are separable by centrifugation in alkaline cesium chloride. Base analyses on the separate strands demonstrate that the two satellite DNA's represent different species.     

New method for detecting cellular transforming genes

Tumor induction in athymic nude mice can be used to detect dominant transforming genes in cellular DNA. Mouse NIH 3T3 cells freshly transfected with either cloned Moloney sarcoma proviral DNA or cellular DNA's derived from virally transformed cells induced tumors when injected into athymic nu/nu mice. Tumors were also induced by cells transfected with DNA from two tumor-derived and one chemically transformed human cell lines. The mouse tumors induced by human cell line DNA's contained human DNA sequences, and DNA derived from these tumors was capable of inducing both tumors and foci on subsequent transfection. Tumor induction in nude mice represents a useful new method for the detection and selection of cells transformed by cellular oncogenes.     

Chromosomal location of human T-cell receptor gene Ti beta

A complementary DNA probe corresponding to the beta-chain gene of Ti, the human T lymphocyte receptor, has been molecularly cloned. The chromosomal origin of the Ti beta gene was determined with the complementary DNA by screening a series of 12 cell hybrid (mouse X human) DNA's containing overlapping subsets of human chromosomes. DNA hybridization (Southern) experiments showed that the human Ti beta gene resides on chromosome 7 and is thus not linked to the immunoglobulin loci or to the major histocompatibility locus in humans.     

Stable amplified DNA in drug-resistant Leishmania exists as extrachromosomal circles

The relative stability of amplified DNA in drug-resistant Leishmania major was previously reported to be dependent on location, that is, unstable amplified DNA was extrachromosomal and stable amplified DNA was chromosomal. Leishmanial chromosomes have now been directly examined by means of orthogonal-field-alternation gel electrophoresis (OFAGE). The amplified DNA's in three resistant cell lines displayed unusual migration and were clearly extrachromosomal, regardless of whether the amplified DNA's were stable or unstable. Thus, contrary to conclusions from earlier studies of drug resistance in cultured animal cells, stable amplified DNA in Leishmania can be extrachromosomal. In addition, these amplified DNA's were shown to be circular on the basis of their resistance to exonuclease III digestion and their behavior on OFAGE. Their mobility was also greatly changed after treatment with topoisomerase II, suggesting that the amplified DNA's were either supercoiled or concatenated circles.     

Cellular transformation by human papillomavirus DNA in vitro

Molecularly cloned DNA's of human papillomaviruses HPV-5 and HPV-l induced morphological transformation of mouse C127 cells in culture. Single-cell clones of cells transformed by papillomavirus contained multiple persistent episomal copies of the transfected DNA species and were analyzed for growth characteristics indicating malignant potential.     

Cytoplasmic Reversion of cms-S in Maize: Association with a Transpositional Event

Spontaneous reversion to fertility in S male-sterile cytoplasm of maize is correlated with the disappearance of the mitochondrial plasmid-like DNA's, S-1 and S-2, and changes in the mitochondrial chromosomal DNA. Hybridization data indicate that one of the plasmid-like DNA's, S-2, is prominently involved in the mitochondrial DNA rearrangements.     

High-efficiency ligation and recombination of DNA fragments by vertebrate cells

DNA-mediated gene transfer (transfection) is used to introduce specific genes into vertebrate cells. Events soon after transfection were quantitatively analyzed by determining the infectivity of the DNA from an avian retrovirus and of mixtures of subgenomic fragments of this DNA. The limiting step of transfection with two DNA molecules is the uptake by a single cell of both DNA's in a biologically active state. Transfected cells mediate ligation and recombination of physically unlinked DNA's at nearly 100 percent efficiency.     

Genetic reconstitution of functional acetylcholine receptor channels in mouse fibroblasts

Foreign genes can be stably integrated into the genome of a cell by means of DNA-mediated gene transfer techniques, and large quantities of homogenous cells that continuously express these gene products can then be isolated. Such an expression system can be used to study the functional consequences of introducing specific mutations into genes and to study the expressed protein in the absence of cellular components with which it is normally in contact. All four Torpedo acetylcholine receptor (AChR) subunit complementary DNA's were introduced into the genome of a mouse fibroblast cell by DNA-mediated gene transfer. A clonal cell line that stably produced high concentrations of correctly assembled cell surface AChR's and formed proper ligand-gated ion channels was isolated. With this new expression system, recombinant DNA, biochemical, pharmacological, and electrophysiological techniques were combined to study Torpedo AChR's in a single intact system. The physiological and pharmacological profiles of Torpedo AChR's expressed in mouse fibroblast cells differ in some details from those described earlier, and may provide a more accurate reflection of the properties of this receptor in its natural environment.     

Molecular biological mechanisms of speciation

Growing recognition that much of the evolutionary history of eukaryotic genomes reflects the operation of turnover processes involving repetitive DNA sequences has led to the recent formulation of models describing speciation as a consequence of such turnover. These models are of three general kinds: those attributing hybrid infertility to the process of transposition, those attributing hybrid infertility to mispairing between chromosomes of divergent repetitive DNA composition, and those assuming that change in repetitive DNA's can reset coordinated gene regulation. These models are discussed with respect to the kinds of evidence needed for their corroboration and to their significance for questions related to macroevolutionary punctuated equilibria and genetic revolutions.     

Selective loss of a family of gene transcripts in a hereditary murine cataract

The eye lens of the Fraser mouse contains a dominantly inherited cataract with reduced amounts of seven distinct but homologous gamma crystallins encoded by a family of gamma-crystallin genes. The results of experiments with cultured lenses, cell-free RNA translation, and Northern blot hybridization indicated a specific loss of the family of gamma-crystallin messenger RNA's in the Fraser mouse lens. Southern blot hybridization of genomic DNA's from normal and Fraser mice showed no differences in gamma-crystallin coding sequences.     

Transcription of nonrepeated DNA in mouse brain

Under normal conditions of DNA renaturation, about 60 percent of mouse DNA fragments renature at a rate consistent with their being present only once per sperm. These nonrepeated sequences (also called single-copy or unique) may be used in RNA-DNA hybridization experiments to provide quantitative estimates of RNA diversity. About 10 percent of the mouse single-copy sequences are transcribed in mouse brain tissue. Estimates of about 3 percent were obtained for mouse liver and kidney RNA's. If only one of the complementary DNA strands is transcribed, this hybridization value implies that the equivalent of at least 300,000 different sequences of 1000 nucleotides are expressed in mouse brain tissue. It is suggested that the large amount of DNA in mammals is functionally important, and that a substantial proportion of the genome is expressed in the brain.     

Replicating form of a single-stranded DNA virus: isolation and properties

The replicating form of single-stranded DNA virus has been isolated in pure form by chromatography on columns of methylated albumin. Its buoyant density in CsCl and "melting temperature" are characteristic of a double stranded DNA structure containing 43 percent guanine-cytosine. The nearest neighbors to uridylate were compared in the RNA synthesized when replicating-form DNA and mature single-stranded DNA were employed as templates in an in vitro system. The mature DNA component of the replicating duplex does not serve as the sole source of complementary RNA. The results agree best with the assumption that both strands of the replicating form function as templates. It is important to note that this is contrary to the situation found in the intact cell where only one of the two strands appears to be transcribed into message.     

Small DNA deletions creating avirulence in Streptococcus pyogenes

The M protein is the antigen on the surface of group A streptococci that allows these bacteria to resist phagocytosis. DNA encoding the M12 protein was cloned into Escherichia coli and used as an isotopically labeled hybridization probe to compare genomic DNA's isolated from M+ and M- isogenic cultures in an effort to elucidate the genetic basis of this variation. DNA's from two spontaneous, independent M- variants contained small (approximately 50 base pairs) deletions which were mapped to identical restriction fragments within or adjacent to the M protein coding sequence. Taken together with the pleiotropic nature of these deletions, this suggests that they define a regulatory switch.     

DNA methylation decreases in aging but not in immortal cells

When normal diploid fibroblasts from mice, hamsters, and humans were grown in culture, the 5-methylcytosine content of their DNA's markedly decreased. The greatest rate of loss of 5-methylcytosine residues was observed in mouse cells, which survived the least number of division. Immortal mouse cell lines had more stable rates of methylation.     

Isolation of human C-reactive protein complementary DNA and localization of the gene to chromosome 1

With a synthetic oligonucleotide mixture as probe, complementary DNA clones of C-reactive protein were isolated from an adult human liver complementary DNA library. The clones ranged in size from 700 to 1100 base pairs and were identified by partial DNA sequence analysis. One complementary DNA clone was used as a probe for hybridization with human-rodent DNA's isolated from somatic cell hybrids and bound to nitrocellulose filters (Southern blot analysis) to assign the human C-reactive protein gene to chromosome 1.     

Assembling materials with DNA as the guide

DNA's remarkable molecular recognition properties and structural features make it one of the most promising templates to pattern materials with nanoscale precision. The emerging field of DNA nanotechnology strips this molecule from any preconceived biological role and exploits its simple code to generate addressable nanostructures in one, two, and three dimensions. These structures have been used to precisely position proteins, nanoparticles, transition metals, and other functional components into deliberately designed patterns. They can also act as templates for the growth of nanowires, aid in the structural determination of proteins, and provide new platforms for genomics applications. The field of DNA nanotechnology is growing in a number of directions, carrying with it the promise to substantially affect materials science and biology.     

A major human histone gene cluster on the long arm of chromosome 1

A human histone gene cluster was assigned to chromosome 1 by Southern blot analysis of DNA's from a series of mouse-human somatic cell hybrids with 32P-labeled cloned human H4 and H3 histone DNA as probes. Localization of this histone gene cluster on the long arm of chromosome 1 was confirmed by in situ hybridization of this DNA probe to metaphase chromosomes.     

Genetic mapping of the mouse proto-oncogene c-sis to chromosome 15

The mouse homolog (c-sis) of the transforming gene of the simian sarcoma virus was mapped to chromosome 15 by the Southern blot analysis of DNA's from hamster-mouse somatic cell hybrids. Alterations in c-sis expression may thus play a role in the various murine neoplastic diseases characterized by rearrangements or duplications of chromosome 15.     

Replication of chloroplast DNA of tobacco

An experimental method has been designed for determining the relative rates of replication of the chloroplast and nuclear DNA's of Nicotiana tabacum. By this method chloroplast DNA in week-old seedlings is being replicated several times faster than nuclear DNA.     

Differentiation of respiratory and abortigenic isolates of equine herpesvirus 1 by restriction endonucleases

Viruses classified by immunologic criteria as equine herpesvirus 1 cause respiratory disease and abortion in horses. Restriction endonuclease analyses of the DNA's of viruses from animals with respiratory disease and from aborted fetuses show that the patterns for respiratory viruses, while similar to each other, are entirely different from the patterns for fetal viruses. It is therefore proposed that the DNA restriction endonuclease patterns of fetal and respiratory viruses analyzed in this study be designated as prototypic of equine herpesvirus 1 and 4, respectively.