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At least 19 recordsLinked to original sources
PubMed1979

The physician assistant in rural primary care practices: physician assistant activities and physician supervision at satellite and non-satellite practice sites.

Nineteen practice sites in Iowa were studied to determine the differences in the types of physician (MD) supervision the physician assistant (PA) received at work at satellite (separate from the major practice site of the supervising MD) and non-satellite practice sites. The MDs supervised PA functions in 12.9 per cent of the patients seen by the PAs at non-satellite and 15.9 per cent of patients they saw at satellite practice sites. All patients with presenting manifestations that suggested life-threatening conditions were seen by MDs at satellite and non-satellite sites. The MD spent 9.2 minutes per patient at satellite clinics, compared to 4.4 minutes per patient at non-satellite clinics. PAs working at satellite sites appeared to receive as much supervision as PAs working at non-satellite clinics.

Clinical Competence↗
PubMed1979

Satellite Ic: a possible link between the satellite DNAs of D. virilis and D. melanogaster.

In this study, we isolated and characterized a previously undetected cryptic satellite DNA comprising 0.1% of the total nuclear genome of D. virilis. This satellite is hidden from detection in neutral CsCl by satellite I and is therefore designated cryptic satellite I or Ic. Sequence analysis reveals that Ic is the repeating heptanucleotide [poly d(AATATAG): d(CTATATT)]. It is more closely related to the three simple sequence satellite DNAs of D. melanogaster, a distantly related species, than it is to any of the major D. virilis satellite DNA sequences. Ic may therefore be a link between the simple sequence satellites of D. virilis and D. melanogaster. As an extension of this theory, we have constructed a "family tree" linking the satellites of D. virilis and D. melanogaster by a series of "simple" operations. Only one intermediate required by this evolutionary scheme has not yet been identified.

Animals↗
PubMed1979

Prominent acrocentric chromosome satellites in child patients with mental retardation or psychiatric disorders; no IQ-satellite size correlation.

Child patients with mental retardation or psychiatric disorders were selected for the presence of prominent acrocentric chromosome satellites and highest or lowest IQ scores. No correlation was found between IQ scores, of which eleven were below IQ 54 and 16 above IQ 68, and the length of acrocentric short arm, satellite, stalk, or short arm material below the stalk. Conventional staining, quinacrine fluorescence, C banding and ammoniacal silver staining revealed the apparent same acrocentric short arm variation between patient and one parent in eight families studied. These findings suggest that the satellite variants were truly normal variants and not etiologically related to the developmental disorders seen in the patients.

Child↗
PubMed1977

The interactions of the separated strands of satellite DNAs with other DNAs: 1. Conditions for associations of the alpha-satellite of the guinea pig with heterologous double-stranded DNAs.

The separated H- and L-strands of the alpha-satellite of the guinea pig, Cavea porcellus, recovered from centrifugation in alkaline CsC1 gradients, from complexes with 7 different double-stranded (ds) DNAs including those of 1 bacteriophage, 2 prokaryotes, 2 invertebrates and 2 mammals. The complexes are not artifacts due to in vitro labeling of the satellite, methods of collection, the presence of divalent cations, or the fact that trace amounts of single-stranded (ss) DNAs are used. More complex dsDNAs, such as that recovered from nicked RF M13, do not associate with dsDNAs.

Animals↗
PubMed1979

Primate repetitive DNAs: evidence for new satellite DNAs and similarities in non-satellite repetitive DNA sequence properties.

Repetitious DNA sequences have been isolated from a number of the primates in in both Suborders Anthropoidea and Prosimii by hydroxy-apatite chromatography at a Cot of 10. In addition to finding previously unreported possible AT-rich satellite DNAs in Orangutan, Gibbon, Rhesus and Slow Loris a clear similarity to human DNA was found in the nonsatellite repetitious DNA sequence properties of the primates in the Suborder Anthropoidea. This is based on the presence of the hydroxyapatitie isolated 1.703 and 1.714 g/cm3 DNA families in CsCl gradients in the analytical ultracentrifuge following renaturation and extensive DNA hyperpolymer network formation. Within the superfamily Hominoidea the amount of the 1.714 g/cm3 DNA family was greater than that of the 1.703 g/cm3 DNA family while the reverse situation was true within the Superfamily Cercopithecoidea. The orangutan 1.703 and 1.714 g/cm3 DNA families were shown to exhibit the same differential reassociation behavior demonstrated previously in human DNA (Marx et al., 1976a). These data are interpreted as preliminary evidence for a similar sequence organization in the Order Primates Suborder Anthropoidea.

Animals↗
PubMed1977

Comparative analysis of three guinea pig satellite DNA's by restriction nucleases.

The structures of guinea pig satellite DNAs I, II, and III have been analyzed by digestion with seven restriction nucleases. From the cleavage patterns it is obvious that the long-range periodicities in these three satellites differ rather characteristically Satellite I is fairly resistant to six nucleases and gives only a number of weak discrete bands which do not show a simple regularity. By the restriction nuclease from Arthrobacter luteus, however, it is cleaved extensively and yields very heterogeneous breakdown products. This is consistent with the high extent of divergence previously found for this satellite, e. g. by sequence analysis. Satellite II is almost completely resistant to all nucleases, indicative of a high degree of sequence homogeneity of this satellite. Satellite III is completely broken by the restriction nuclease from Bacillus subtilis into fragments which form a novel, highly regular series of bands in gel electrophoresis. The patterns show that the satellite is composed of tandem repeats ofapproximately 215 nucleotide pairs length, each repeat unit containing two cleavage sites for this nuclease. The data are consistent with the assumption that 30--40% of all cleavage sites have been eliminated by a random process. Satellite III DNA yields weak degradation patterns of the same periodicity with a number of other restriction nucleases. Cleavage sites for these nuclease are clustered on separatesmall segments of the satellite DNA. In this respect, the satellite is similar to others, notably the mouse satellite DNA. The three guinea pig satellites are examples of more general types of satellite structures also found in othe organisms. Similarities and differences to other satellites are discussed with special consideration to theories on the evolution of this class of DNA.

Animals↗
PubMed1978

Analysis of plant genomes. IV. Isolation and characterization of satellite DNA components from two dicotyledons cucumber (Cucumis sativus) and radish (Raphanus sativus).

Satellite DNA fractions from cucumber and radish, two plants having low DNA contents and relatively small chromosomes, were isolated and characterized. Reassociation studies of satellite and total nuclear DNA showed that the satellite fractions in these two plants contain most of the rapidly reassociating DNA. Cucumber satellite I was found to contain one major component (70% of the total satellite) having a density of 1.706 g/cm3 and a Tm of 90.5 degrees C and a minor component with a density of 1.712 g/cm3 and a Tm of 93.5 degrees C. The complexity of the major component was estimated to be 3.8 X 10(5) daltons while that of the minor one was 12.9 X 10(7) daltons. Although cucumber satellite II banded as a single peak at a density of 1.700 g/cm3 in neutral CsCl gradients, it was observed to have a rather broad denaturation profile with a Tm of 86.5 degrees C. Its Cot curve was also broader than that of satellite I and one of its components (40% of the total) had a complexity of 5.8 X 10(5) daltons. Two satellite fractions were also observed in the case of radish DNA but only satellite I was isolated in a pure form and characterized. This radish satellite formed a sharp, symmetrical peak at a density of 1.698 g/cm3 in neutral CsCl gradients and underwent denaturation in a narrow temperature range of 6 to 7 degrees C. An analysis of the optical reassociation kinetics showed that this satellite contained a major and a minor component. The major component, which comprised 80% of the satellite, had a complexity of 12.9 X 10(5) daltons. Hybridization experiments revealed that the ribosomal DNA was present in satellite II.

Centrifugation, Density Gradient↗
PubMed1978

Conservation and chromosomal localization of DNA satellites in balenopterid whales.

DNA satellites were isolated from three balenopterid species, viz. the minke, sei, and fine whales. In each of them at least two DNA satellites were recognizable with buoyant densities in neutral CsCl of rho = 1.702/1.703 and rho = 1.710/1;711, respectively. cRNAs from each satellite group were used for filter and in situ hybridisations. Homo-and heterologous DNA-cRNA hybrids within each satellite group yielded virtually identical melting curve profiles showing conservation of at least a considerable part of the DNA satellite sequences. There was no evident sequence homology between the rho = 1.702/1.703 and the rho = 1.710/1;711 satellites by filter hybridisation.--The in situ hybridisation showed that in each species the rho = 1.702/1.703 satellite was located in centromeric-paracentromeric C-bands in a few pairs, whereas the rho = 1.710/1.711 satellite was located in terminal C-bands throughout the karyotypes.--The data on the whale DNA satellites indicate that the quantitative evolution of the sateliite DNA sequences preceded species divergence of the balenopterids and that the satellite sequences have remained relatively unaltered since the divergence took place. The function of satellite DNA is considered to imply the introduction of both chromosomal and genic polymorphisms and thus being of great importance in speciation, Based upon these concepts a model is postulated for the function of satellite DNA. According to this model at meiotic pairing euchromatinheterochromatin overlapping between homologous chromosomes is considered to be of a general occurrence. This overlapping is presumed to be accentuated by the size heteromorphism frequently observed between homologous heterochromatic segments (C-bands). In the region of such euchromatinheterochromatin overlapping, cross-over would be excluded. The overlapping is suggested to be rectified progresssively in the chromosome arms, leaving unaffected crossing-over distant to the euchromatin-heterochromatin junctions. The consequence of this will be that genes in the proximity of the junctions are collectively inherited and selected, whereas genes distant to the the heterochromatin will be independently assorted and selected.

Animals↗
PubMed1979

Behaviour of sex chromosome associated satellite DNAs in somatic and germ cells in snakes.

Sex chromosome associated satellite DNAs is isolated from the snakes Elaphe radiata (sat III) (Singh et al., 1976) and Bungarus fasciatus (Elapidae) (minor satellite) are evolutionarily conserved throughout the suborder Ophidia. An autosome limited satellite DNA (B. fasciatus major satellite) is not similarly conserved. Both types of satellites have been studied by in situ hybridisation in various somatic tissues and germ cells where it has been observed that the W sex chromosome remains condensed in interphase nuclei. In growing oocytes however, the W chromosome satellite rich heterochromatin decondenses completely whilst the autosomal satellite rich regions remain condensed. Later, the cycle is reversed and the W chromosome condenses whilst the autosomal satellite regions decondense. In a primitive snake (Eryx johni johni) where the sex chromosomes are not differentiated and where there is no satellite DNA specific to them, these phenomena are absent. - The differential behaviour of autosomal and sex chromosome associated satellite DNAs is discussed in the light of gene regulation.

Animals↗
PubMed1978

Correlation between phosphorylated H1 histones and satellite DNAs in Drosophila virilis.

Drosophila virilis DNA contains satellites I, II, and III. D. novamexicana DNA contains satellite I. D. virilis H1 histone contains subfractions a, b, c, d, and e; D. novamexicana H1 contains subfractions a, b, and c. Therefore, satellites II and III might be correlated with H1d and H1e. To test the validity of this correlation, the H1 histones of polytene nuclei, which contain less than 1% satellite DNA, were analyzed. Polytene nuclei of D. virilis contain substantially decreased levels of H1c and H1e and marginally decreased levels of H1d. Polytene nuclei of D. novamexicana contain decreased levels of H1c.H1c is correlated with satellite I (common to D. virilis and D. novamexicana); H1e is correlated with satellites II and III; H1d is not correlated with any satellite DNA, because its level is virtually unchanged in polytene cells lacking detectable amounts of satellite DNA. Alkaline phosphatase digestion of the H1 histones reveals that H1c is the phosphorylated form of H1b and H1e is the phosphorylated form of H1d. Therefore, the under-replication of satellite DNAs is correlated with the decreased phosphorylation of H1 histones. In vitro, D. virilis H1 histones preferentially bind D. virilis DNAs in the progression III greater than II greater than I greater than main band, whereas D. virilis core histones do not preferentially bind any D. virilis DNA. As an extension of these results, we suggest that phosphorylated H1 histones bind D. virilis satellite DNAs in vivo and are involved in the compaction of heterochromatin.

Alkaline Phosphatase↗
PubMed1976

Cloning of calf thymus satellite I DNA in Escherichia coli.

The 1400 base pair repeat produced by digestion of calf satellite I DNA (phi = 1.714 g/cm3) with EcoRI, was cloned in E. coli. The hybrid plasmid (pGM 214) which contains the ColE1-Ap vector (pSF 2124) and the 1400 base pair fragment replicates stably in E. coli and can be amplified by chloramphenicol treatment. No clone was found in which more than one "repeat unit" of the satellite I DNA was present in the chimaera plasmid. Digestion of the original satellite I and the plasmid pGM 214 with R-SmaI shows that the satellite DNA replicated in E. coli is cleaved by the restriction endonuclease SmaI whereas the original satellite I DNA from calf thymus is not, suggesting that the satellite I contains a large amount of modified cytosine or guanosine, probably 5-methyl-cytosine. R-EcoRI* produces a number of fragments with the satellite I in the range of 300 base pairs to 1400 base pairs. A physical map of pGM 214 (and pSF 2124) with R-EcoRI, R-HincII, R-HindIII, R-SmaI, R-BamI and R-EclI was constructed. The 1400 base pair "repeat unit" in the pGM 214 is efficiently transcribed in vitro by purified RNA polymerase, starting from a pSF 2124 promoter. The restriction enzyme EclI produces a 350 base pair repeat with calf satellite II (phi = 1,722 g/cm3), whereas the satellite I is not cut by this enzyme.

Animals↗
PubMed1978

Genetic studies on heterochromatin in Drosophila melanogaster and their implications for the functions of satellite DNA.

In Drosophila melanogaster the centromeric heterochromatin of all chromosomes consists almost entirely of several different satellite DNA sequences. In view of this we have examined by genetic means the meiotic consequences of X chromosomes with partial deletions of their heterochromatin, and have found that the amount and position of recombination on each heterochromatically deleted X is substantially different from that of a normal X. It appears that the amount of heterochromatin is important in modifying the "centromere effect" on recombination.--In all the deleted Xs tested, chromosome segregation is not appreciably altered from that of a nondeleted control chromosome. Thus satellite DNA does not appear to be an important factor in determining the regular segregation of sex chromosomes in Drosophila. Additionally, since X chromosomes with massive satellite DNA deficiencies are able to participate in a chromocenter within salivary gland nuclei, a major role of satellite DNA in chromocenter formation in this tissue is also quite unlikely.--In order to examine the mechanisms by which the amount of satellite DNA is increased or decreased in vivo, we have measured cytologically the frequency of spontaneous sister chromatid exchanges in a ring Y chromosome which is entirely heterochromatic and consists almost exclusively of satellite DNA. In larval neuroblast cells the frequency of spontaneous SCE in this Y is approximately 0.3% per cell division. Since there is no meiotic recombination in D. melanogaster males and since meiotic recombination in the female does not occur in heterochromatin, our results provide a minimum estimate of the in vivo frequency of SCE in C-banded heterochromatin (which is predominantly simple sequence DNA), without the usual complications of substituted base analogs, incorporated radioactive label or substantial genetic content.--We emphasise that: (a) satellite DNA is not implicated in any major way in recognition processes such as meiotic homologue recognition or chromocenter formation in salivaries, (b) there is likely to be continuous variation in the amount of satellite DNA between individuals of a species; and (c) the amount of satellite DNA can have a crucial functional role in the meiotic recombination system.

Animals↗
PubMed1977

Analysis of the alpha-satellite DNA from African green monkey cells by restriction nucleases.

By the use of restriction endonucleases the organization of the alpha-satellite DNA from African green monkey cells (Cercopithecus aethiops) has been analyzed. With endo R-HindIII, endo R-AluI and with endo R-EcoRI at conditions of low salt and high pH (endo R-EcoRI) all of the satellite was digested while only a part of the satellite was cleaved with endo R-Bsu and endo R-EcoRI under standard conditions. With each of the four nucleases a series of fragments was formed which were multiplies in size of a basic repeat unit linked in tandem arrays in the intact satellite. The quantitative evaluation of the digestion with each nuclease as well as with combinations of two nucleases yielded information about the distribution of the cleavage sites. While the arrangement of the endo R-HindIII cleavage sites conforms to a random distribution across the entire satellite, the results from the endo R-Bsu and endo R-EcoRI cleavage patterns are consistent with a picture where the cleavage sites are clustered in fractions of the satellite. Since endo R-AluI recognizes the central four nucleotide pairs of the endo R-HindIII cleavage site, the redigestion of the endo R-HindIII dimer with endo R-AluI gave information about the distribution of mutations in the satellite. The results of these experiments together with the comparison of the sequence divergence determined from digestion with endo R-HindIII and endo R-EcoRI lend support to the hypothesis that mutations have affected all bases in the satellite evenly. The gamma-satellite, another fraction of the African green monkey DNA, could be separated by Ag+/CsSO4 density gradient centrifugation into two components. With the three restriction nucleases used both components gave a background of fragments of heterogenous length on gel electrophoresis with some faint bands of no apparent regularity in one case.

Animals↗
PubMed1977

Analysis of calf-thymus satellite DNA: evidence for specific methylation of cytosine in C-G sequences.

Digestion of purified calf tymus satellite I (phi = 1.714 g/cm3) with a series of restriction enzymes shows that modification in this satellite occurs preferentially in the sequence C-G. This was also shown to be the case in the other satellites and in bulk chromosomal calf thymus DNA. Cloning of purified satellite I DNA in Escherichia coli makes sites, previously modified, available for cutting with certain restriction enzymes. All these 'new sites' contain the sequence C-G. High-resolution mass spectros-copy establishes that the satellites contain a low concentration of 5-methylcytosine. This infers that methylation which inhibits retriction enzyme cutting must occur preferentially in the sequence C-G. Hybridization of cRNA of cloned satellite I DNA with the satellites III (phi = 1.706 g/cm3) and IV (phi = 1.710 g/cm3) shows that there is no or little sequence homology between these satellites. Digestion of calf thymus satellite I DNA with endoR. EcoRI and subsequent hybridization studies with the fragments shows two EcoRI fragments in addition to the usual 1400-base-pair EcoRI repeat unit.

Animals↗
PubMed1978

The distribution of satellite and main-band DNA components in the melanogaster species subgroup of Drosophila. I. Fractionation of DNA in actinomycin D and distamycin A density gradients.

Fractionation of total adult DNA of five of the seven species of the melanogaster species sub-group of Drosophila in actinomycin D and distamycin A caesium density gradients has revealed the presence of three main-band DNA components, common to all species, and ten satellite DNAs that are distributed between the species. Satellite DNAs are either unique to a species or common to two or more species. The abundance of a common satellite DNA varies between species. There is no simple relationship between the presence of a satellite DNA and a branch point of phylogenetic divergence; nevertheless the arrangement of the species in a phylogeny that is based on the numbers of satellites held in common accurately reflects the pattern of relationships between the same species based on differences in inversions of polytene chromosomes. The species can be similarly arranged according to the compositions of their mitochondrial DNAs. It is possible that the same basic set of sequences, each of low frequency, is common to all species with arbitrary or selected amplification of particular sequences to differing extents in individual species. The conservation of satellites in the group and the close parallel between the distributions of satellites and inversions between the species suggests that either the processes that operate to change both chromosomal phenomena are similarly time-dependent and occurring at relatively low rates or that their rates of change are restricted according to some undetermined functions of these aspects of the genome.

Animals↗
PubMed1979

Molecular cytogenetics of the Equidae. I. Purification and cytological localization of a (G + C)-rich satellite DNA from Equus przewalskii.

A (G + C)-rich density satellite DNA (rho = 1.713 gm/cc) has been purified from splenic DNA of Przewalski's horse, Equus przewalskii, by successive equilibrium density gradient centrifugations. The purified satellite, which may comprise as much as 29% of the total DNA, renatures rapidly; however, analyses of native, single-stranded, and reassociated molecules by analytical ultracentrifugation and melting properties suggest that some sequence heterogeniety exists in the 1.713 gm/cc satellite. Complementary RNA (cRNA) transcribed from satellite DNA has been utilized for in situ hybridization studies with E. przewalskii metaphase chromosomes previously identified by quinacrine-banding. These studies establish that sequences complementary to the 1.713 g/cc satellite are greatly enriched in the centromeres of some, but not all, chromosomes. The differential distribution of satellite DNA sequences over heterochromatic regions allows discrimination of three classes of heterochromatin and serves to define three types of pericentromeric regions in the karyotype of this endangered equine species. Additionally, apparent polymorphism in concentrations of satellite DNA sequences between homologs in the same karyotype is noted.

Animals↗
PubMed1978

Analysis of plant genomes. III. Denaturation and reassociation properties of cryptic satellite DNAs in barley (Hordeum vulgare) and wheat (Triticum aestivum).

A cryptic satellite fraction was isolated from barley and wheat by preparatory ultracentrifugation of total DNA in Ag+-Cs2SO4 density gradients and was characterized by studying its denaturation-reassociation properties. Wheat satellite DNA underwent thermal denaturation as a single component with a Tm of 81 degrees C while barley satellite DNA consisted of one major (Tm = 82.5 degrees C) and one minor (Tm = 91 degrees C) component. When the barley and wheat satellites were reassociated and then melted, the Tm values were found to be 6--7 degrees C lower than those of the corresponding native DNA preparations. Examination of the C0t curves of these two satellite DNAs revealed the presence of a major, fast reassociating and a minor, slow reassociating fraction. The fast reassociating DNA fraction of barley was found to have a complexity of 9.7 . 10(5) daltons while that of wheat satellite was 5.8 . 10(5) daltons. Since these satellites reassociated with about 4--5% base mismatching, as judged by their deltsTm (6--7 degrees C), they each appear to consist of rather similar base sequences.

Centrifugation, Density Gradient↗