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M F Singer

Publications and source records attributed to M F Singer.

At least 55 records · Page 3Linked to original sources
PubMed1982

A monkey Alu sequence is flanked by 13-base pair direct repeats by an interrupted alpha-satellite DNA sequence.

A member of the Alu family, the dominant family of short interspersed repeated DNA sequences in primates, interrupts a cloned repeat unit of African green monkey alpha-satellite DNA. The Alu is immediately flanked by 13-base-pair duplications of the known sequence of the satellite at the site of insertion. These observations support the idea that Ala family members may be moveable elements.

Animals↗
PubMed1981

Interspersed repeated sequences in the African green monkey genome that are homologous to the human Alu family.

The dominant family of interspersed repetitive DNA sequences in the human genome has been termed the Alu family. We have found that more than 75% of the lambda phage in a recombinant library representing an African green monkey genome hybridize with a human Alu sequence under stringent conditions. A group of clones selected from the monkey library with probes other than the Alu sequence were analyzed for the presence and distribution of Alu family sequences. The analyses confirm the abundance of Alu sequences and demonstrate that more than one repeat unit is present in some phages. In the clones studied, the Alu units are separated by an average of 8 kilobase pairs of unrelated sequences. The nucleotide sequence of one monkey Alu sequence is reported and shown to resemble the human Alu sequences closely. Hence, the sequence, dispersion pattern, and copy number of the Alu family members are very similar in the African green monkey and human genomes. Among the clones investigated were two that contain segments of the satellite DNA term alpha-component joined to non alpha-component DNA. The experiments indicate that in the monkey genome Alu sequences can occur close to regions of alpha-component DNA.

Animals↗
PubMed1981

Sequence relationships between single repeat units of highly reiterated African Green monkey DNA.

Individual monomer and dimer units of the highly repeated alpha-component DNA of African Green monkeys were isolated and amplified by molecular cloning in pBR322. The purified sequences were characterized by digestion with restriction endonucleases and by primary nucleotide sequence analysis. Comparison of the cloned units with the 172 base pair long sequence representing the most abundant nucleotide at each position in the set of sequences comprising alpha-component allows the following conclusions. The set of sequences comprising alpha-component is made up of a very large number of related but slightly divergent sequences. Two neighboring repeats of the monomer unit are not necessarily more similar to one another than are randomly isolated monomers.

Animals↗
PubMed1981

DNA sequences similar to those around the simian virus 40 origin of replication are present in the monkey genome.

We report the molecular cloning of African green monkey genomic DNA segments that include regions of homology to the origin of replication of simian virus 40 (SV40). Three clearly different cloned segments 14 to 17 kilobase pairs (kb) long were isolated from a genomic library in lambda phage. We estimate that each of the three is repeated fewer than four times in the monkey genome. The SV40-like regions represent a small portion of the cloned segments, and these regions cross hybridize only weakly with one another. One of the three segments is described here in detail. Although the entire segment occurs only once or twice in the monkey genome, it contains DNA sequences (other than the SV40-like sequences) that are repeated elsewhere in the genome including in the other two cloned segments. The homology to SV40 is contained within about 300 base pairs of monkey DNA and is limited to the region around the viral replication origin. The nucleotide sequence of the SV40-like region was determined. It contains a large number of short stretches homologous to three specific noncoding domains around the SV40 origin of replication: the 27-base-pair region of dyad symmetry, the first set of (short) repeats that occur just on the late side of the origin, and, further in the late direction, the two 72-base-pair-long repeats. Although these components are grouped in the monkey DNA, as they are in SV40 DNA, their relative juxtaposition is scrambled.

Animals↗
PubMed1981

Recurring defective variants of simian virus 40 containing monkey DNA segments.

Four independently and newly isolated defective variants of simian virus 40 have been characterized. All four are very similar, if not identical, to two previously and independently isolated variants (Wakamiya et al., J. Biol. Chem. 254:3584-3591, 1979; J. Papamatheakis, E. Kuff, E. Winocour, and M. F. Singer, J. Biol. Chem. 255:8919-8927, 1980). The documented similarities include restriction endonuclease maps and the presence of the same monkey DNA segments covalently linked to simian virus 40 DNA sequences. Each of the newly described variants was first detected upon serial passaging of wild-type simian virus 40 at a high multiplicity of infection at 33 degrees C as recently described (M. F. Singer and R. E. Thayer, J. Virol. 35:141-149, 1980). A variety of experiments support the idea that the various isolates were independent and do not reflect inadvertent cross-contamination. Two of the new isolates arose during passage of wild-type strain 777 virus in BSC-1 cells, one during passage of strain 776 in BSC-1 cells, and one during passage of strain 776 in primary African green monkey kidney cells. The two variants obtained after passage of strain 776 were shown to contain a particular recognition site for restriction endonuclease MboII within their simian virus 40 DNA segments, as do the two previous isolates. This site is not present in wild-type strain 776 DNA but is shown here to be present in wild-type strain 777 DNA. The surprising recurrence of closely related variants and particularly the unexpected presence of the endo R.MboII site in variants derived from passaging strain 776 suggest that these variants may arise by mechanisms other than recombination between the initial infecting viral genome and the host DNA.

Animals↗
PubMed1981

Three segments from the monkey genome that hybridize to simian virus 40 have common structural elements.

Three cloned segments that hybridize to a region of simian virus 40 (SV40) deoxyribonucleic acid including the origin of replication have been isolated from a monkey genomic library. The primary structure of one segment was previously reported (T. McCutchan and M. Singer, Proc. Natl. Acad. Sci. U.S.A. 78:95-99, 1981). We report here the sequences of the other two segments and a comparison of all three. The SV 40-hybridizing region in each segment is limited to several hundred base pairs. All of the segments contain multiple and disconnected sequences homologous to the region of SV40 directly surrounding the viral replication origin. The number and arrangement of the homologous sequences is different in the three segments. However, the segments have the following features in common: (i) each contains multiple copies of the sequence GGGCGGPuPu, which also appears six times near the origin of SV40; (ii) each contains several strong homologies to the central dyad symmetry of SV40; (iii) each contains a long internal repeat, as does the origin region of SV40. The three SV40-hybridizing segments are members of a larger family of genomic sequences that hybridize well to each other, but not necessarily to SV40.

Animals↗
PubMed1980

Preferential replication of a class of host-substituted defective simian virus 40 variants at low temperature.

The host-substituted variant termed CVP8/1/P2 (EcoRI res) was first isolated several years ago after serial passage of simian virus 40 strain 777 on BSC-1 cells at 37 degrees C. When BSC-1 are coinfected with wild-type simian virus 40 strain 777 and variant CVP8/1/P2 (EcoRI res), the variant rapidly becomes the dominant species produced, often representing as much as 80% of the total DNA I synthesized after infection. We present evidence that the replicative advantage of the variant was increased when the infection was carried out at 33 rather than 37 degrees C. Also described are nine new and independent serial passage experiments carried out at 33 degrees C with several purified wild-type virus stocks, including strain 776, and both BSC-1 and primary African green monkey kidney cells. In each series variants related to CVPs/1/P2 (EcoRI res) were detected in the progeny viral genomes after four serial passages. Hybridization data suggest that at least some of these variant DNA I molecules contain simian virus 40 DNA sequences, monkey alpha-component DNA sequences (highly repetitive), and the infrequently reiterated monkey DNA sequences found in CVP8/1/P2 (EcoRI res), all covalently linked as in CPV8/1/P2 (EcoRI res). It appears that this type of variant emerges with some frequency during infection and is then preferentially replicated at 33 degrees C, thereby becoming readily detectable in passaged stocks. A variety of control experiments indicated that the repeated emergence of similar, if not identical, variants is unlikely to be the result of inadvertent cross-contamination or the presence of detectable amounts of the variant in the plaque-purified viral stocks.

Animals↗
PubMed1978

Comparison of two viable variants of simian virus 40.

The DNAs of two viable strains of simian virus 40, 776 and 777, have been compared by using restriction endonucleases. Differences between the two strains were detected at five separate points on the simian virus 40 genome. One of these differences, in the region of DNA coding for the major viral coat protein, was confirmed by tryptic peptide analysis of coat proteins from the two strains. Some physiological differences between the two strains were examined and can, in general, be explained by differences observed between the DNAs of the two strains. In addition, defective variants derived from strain 777 interfere more efficiently with the replication of strain 777 than with the replication of strain 776.

DNA Restriction Enzymes↗
PubMed1977

Studies on a defective variant of simian virus 40 that is substituted with DNA sequences derived from monkey. II. Structure of DNA.

The structure of a substituted, reiterated defective variant of the simian virus 40 genome has been analyzed. The DNA of the defective variant is a closed circular duplex resistant to restriction endonuclease R-EcoRI and slightly shorter than the genome of wild type simian virus 40. Analysis of the double-stranded DNA segments produced by the action of a variety of restriction endonucleases on the defective genome allow description of the molecule as follows. (a) The full DNA molecule contains four tandem repeats of a DNA segment containing both SV40 and monkey DNA sequences. (b) Three out of the four segments are identical and are about 23% of the wild type genome in length: one segment of the four is larger and contains an additional peice of DNA about 4.3% of a wild type genome in length, but is otherwise identical with the other three segments. (c) Portions of the defective variant that contain monkey DNA can be isolated as discrete segments by restriction endonuclease digestion. (d) Some of the sequences originating from monkey DNA are derived from the highly reiterated class of monkey DNA sequences; others may represent sequences derived from infrequently reiterated or single copy monkey sequences.

Animals↗
PubMed1977

The effect of H1 histone on the action of DNA-relaxing enzyme.

The action of DNA-relaxing enzyme on H1-DNA complexes was investigated. Complexes of superhelical and relaxed closed circular duplex DNA with H1 were treated with mammalian relaxing enzyme, deproteinized, and electrophoresed on agarose gels. At relatively low ratios of H1 to superhelical DNA, molecules of superhelical density intermediate between those of the starting material and relaxed DNA, the normal product, were generated. At relatively high H1 histone concentrations (H1:DNA greater than 0.4 w/w), the superhelical DNA was not relaxed. Further, no superhelical turns were introduced into relaxed closed duplex DNA at any concentration of H1 tested. Thus, the binding of H1 histone to DNA prevents the action of the relaxing enzyme. Moreover, H1 histone does not appear to unwind the DNA duplex upon binding. The implications of these observations and the previously demonstrated specificity of H1 histone for superhelical DNA are discussed in relation to the structure of chromatin.

DNA, Circular↗
PubMed1977

Histone synthesis during infection of monkey kidney cells with Simian Virus 40.

The synthesis of histones during lytic infection of BSC-1 (African Green Monkey kidney) cells with SV40 has been investigated. The synthesis of all five classes of histones was stimulated, and all classes appeared to be stimulated to the same extent. The increase in rate of histone synthesis in response to SV40 infection was detectable several hours before SV40 DNA synthesis was measureable, and the rate of histone synthesis decreased at a time when SV40 DNA synthesis was occuring at a maximal or relatively high rate. In addition, the changes in rates of histone synthesis did not correlate well with the rates of host DNA synthesis during infection. Thus it appears that DNA synthesis and histone synthesis may not be strictly coupled in SV40 infected cells.

Cell Line↗
PubMed1976

H5 Histone and DNA-relaxing enzyme of chicken erythrocytes. Interaction with superhelical DNA.

The interaction of closed circular duplex DNA with the lysine-rich H5 histone fraction of avian erythrocytes has been studied. H5, like H1 histone, interacts preferentially with superhelical DNA. The extent of interaction increases with increasing negative or positive superhelicity. Salt-extracted lysine-rich histones show the same specificity for interaction with superhelices as do acid-extracted preparations. Chicken erythrocyte nuclei contain DNA-relaxing enzyme. This enzyme is extracted from the nuclei at lower salt concentrations than those required to extract H1 and H5 histones and is, therefore, probably a function of a protein distinct from H1 and H5 histones.

Animals↗
PubMed1976

The effect of superhelicity on the interaction of histone f1 with closed circular duplex DNA.

A set of covalently closed circular duplex simian virus 40 DNA preparations of varying superhelical densities was prepared by closure of nicked duplex DNA with polynucleotide ligase in the presence of varying amounts of ethidium. The resulting molecules were tested for complex formation with the lysine-rich histone f1. The results confirmed earlier experiments in demonstrating that f1 histone reacts preferentially with superhelical DNA compared to relaxed circular DNA. Furthermore, the extent of the reaction is demonstrated to depend on the superhelical density. At the relatively low ratios of histone to DNA used in these experiments, the product of the interaction of f1 histone with superhelical DNA does not precipitate. At higher ratios of histone to DNA, an insoluble aggregate is formed.

DNA, Circular↗