Published in Cell on July 01, 1981
A safe packaging line for gene transfer: separating viral genes on two different plasmids. J Virol (1988) 7.87
Patterns of integration of DNA microinjected into cultured mammalian cells: evidence for homologous recombination between injected plasmid DNA molecules. Mol Cell Biol (1982) 7.49
Organization, distribution, and stability of endogenous ecotropic murine leukemia virus DNA sequences in chromosomes of Mus musculus. J Virol (1982) 6.56
Complete nucleotide sequence of the Drosophila transposable element copia: homology between copia and retroviral proteins. Mol Cell Biol (1985) 5.44
Rearrangement and mutagenesis of a shuttle vector plasmid after passage in mammalian cells. Proc Natl Acad Sci U S A (1983) 3.90
DNA insertion in the first intron of maize Adh1 affects message levels: cloning of progenitor and mutant Adh1 alleles. Proc Natl Acad Sci U S A (1984) 3.89
Retrovirus integration and chromatin structure: Moloney murine leukemia proviral integration sites map near DNase I-hypersensitive sites. J Virol (1987) 3.45
Genetic control of intrachromosomal recombination in Saccharomyces cerevisiae. I. Isolation and genetic characterization of hyper-recombination mutations. Genetics (1988) 3.37
Nonreciprocal exchanges of information between DNA duplexes coinjected into mammalian cell nuclei. Mol Cell Biol (1985) 3.00
Molecular cloning and characterization of hepatitis A virus cDNA. Proc Natl Acad Sci U S A (1983) 2.92
A small region of the mouse mammary tumor virus long terminal repeat confers glucocorticoid hormone regulation on a linked heterologous gene. Proc Natl Acad Sci U S A (1983) 2.79
Intracisternal A-particle genes as movable elements in the mouse genome. Proc Natl Acad Sci U S A (1983) 2.76
A linkage map of endogenous murine leukemia proviruses. Genetics (1990) 2.60
Transcriptionally active genome regions are preferred targets for retrovirus integration. J Virol (1990) 2.59
The leader sequence of the subgenomic mRNA's of Rous sarcoma virus is approximately 390 nucleotides. J Virol (1982) 2.51
Adaptation of a retrovirus as a eucaryotic vector transmitting the herpes simplex virus thymidine kinase gene. Mol Cell Biol (1982) 2.51
Flat revertants isolated from Kirsten sarcoma virus-transformed cells are resistant to the action of specific oncogenes. Proc Natl Acad Sci U S A (1983) 2.44
Mutant immunoglobulin genes have repetitive DNA elements inserted into their intervening sequences. Proc Natl Acad Sci U S A (1982) 2.44
Insertion of retrovirus into the first intron of alpha 1(I) collagen gene to embryonic lethal mutation in mice. Proc Natl Acad Sci U S A (1984) 2.30
Divergence and differential expression of soybean actin genes. EMBO J (1985) 2.21
Versatile cosmid vectors for the isolation, expression, and rescue of gene sequences: studies with the human alpha-globin gene cluster. Proc Natl Acad Sci U S A (1983) 2.14
Quantitative analysis of gene suppression in integrated retrovirus vectors. Mol Cell Biol (1986) 2.08
Proviral deletions and oncogene base-substitutions in insertionally mutagenized c-myc alleles may contribute to the progression of avian bursal tumors. Proc Natl Acad Sci U S A (1984) 2.02
Inactivation of p53 gene expression by an insertion of Moloney murine leukemia virus-like DNA sequences. Mol Cell Biol (1984) 2.00
Retrovirus transduction: segregation of the viral transforming function and the herpes simplex virus tk gene in infectious Friend spleen focus-forming virus thymidine kinase vectors. Mol Cell Biol (1983) 1.94
Cloned endogenous retroviral sequences from human DNA. Proc Natl Acad Sci U S A (1982) 1.94
Patterns of proviral insertion and deletion in avian leukosis virus-induced lymphomas. J Virol (1986) 1.93
Effects of Ty insertions on HIS4 transcription in Saccharomyces cerevisiae. Mol Cell Biol (1984) 1.92
Insertion of several different DNAs in reticuloendotheliosis virus strain T suppresses transformation by reducing the amount of subgenomic mRNA. J Virol (1986) 1.83
Replication-competent Moloney murine leukemia virus carrying a bacterial suppressor tRNA gene: selective cloning of proviral and flanking host sequences. Proc Natl Acad Sci U S A (1985) 1.81
Identification of cellular promoters by using a retrovirus promoter trap. J Virol (1989) 1.79
High-frequency deletion in recovered retrovirus vectors containing exogenous DNA with promoters. J Virol (1984) 1.73
Nucleotide sequences of the murine retrovirus Friend SFFVp long terminal repeats: identification of a structure with extensive dyad symmetry 5' to the TATA box. Nucleic Acids Res (1982) 1.70
Human cells infected with retrovirus vectors acquire an endogenous murine provirus. J Virol (1990) 1.65
Variable stability of a selectable provirus after retroviral vector gene transfer into human cells. Mol Cell Biol (1986) 1.62
Retroviral insertions 90 kilobases proximal to the Evi-1 myeloid transforming gene activate transcription from the normal promoter. Mol Cell Biol (1991) 1.61
Association of the lethal yellow (Ay) coat color mutation with an ecotropic murine leukemia virus genome. Proc Natl Acad Sci U S A (1983) 1.60
Transposition of two different intracisternal A particle elements into an immunoglobulin kappa-chain gene. Mol Cell Biol (1984) 1.55
Early postimplantation embryo lethality due to DNA rearrangements in a transgenic mouse strain. Proc Natl Acad Sci U S A (1986) 1.48
Variation in the number of copies and in the genomic organization of ecotropic murine leukemia virus proviral sequences in sublines of AKR mice. J Virol (1982) 1.44
Isolation of duplicated human c-src genes located on chromosomes 1 and 20. Mol Cell Biol (1985) 1.39
Dilute-coat-color locus of mice: nucleotide sequence analysis of the d+2J and d+Ha revertant alleles. Mol Cell Biol (1984) 1.39
Somatic and germ-line reverse mutation rates of the retrovirus-induced dilute coat-color mutation of DBA mice. Proc Natl Acad Sci U S A (1988) 1.39
A complex gene superfamily encodes actin in petunia. EMBO J (1987) 1.31
Molecular markers for the agouti coat color locus of the mouse. Genetics (1987) 1.30
Transforming Sloan-Kettering viruses generated from the cloned v-ski oncogene by in vitro and in vivo recombinations. J Virol (1986) 1.27
Endogenous xenotropic murine leukemia virus-related sequences map to chromosomal regions encoding mouse lymphocyte antigens. J Virol (1984) 1.23
Nucleotide sequence analysis of a variant human T-cell leukemia virus (HTLV-Ib) provirus with a deletion in pX-I. J Virol (1985) 1.23
Immunoglobulin heavy chain switch region recombination within a retroviral vector in murine pre-B cells. EMBO J (1987) 1.19
Bidirectional transcription from a solo long terminal repeat of the retrotransposon TED: symmetrical RNA start sites. Mol Cell Biol (1986) 1.16
Retroviral insertional mutagenesis of a target allele in a heterozygous murine cell line. Proc Natl Acad Sci U S A (1985) 1.07
Retrovirus promoter-trap vector to induce lacZ gene fusions in mammalian cells. J Virol (1991) 1.07
Genome structure and thymic expression of an endogenous retrovirus in zebrafish. J Virol (2004) 1.07
Identification of a provirally activated c-Ha-ras oncogene in an avian nephroblastoma via a novel procedure: cDNA cloning of a chimaeric viral-host transcript. EMBO J (1986) 1.06
Evidence for mobility of a new family of mouse middle repetitive DNA elements (LTR-IS). Nucleic Acids Res (1984) 1.03
Two different types of transcription for the myelocytomatosis viruses MH2 and CMII. EMBO J (1983) 1.01
Revertants and partial transformants of rat fibroblasts infected with Fujinami sarcoma virus. J Virol (1984) 0.98
Cellular DNA rearrangements and early developmental arrest caused by DNA insertion in transgenic mouse embryos. Mol Cell Biol (1987) 0.97
Global Manufacturing of CAR T Cell Therapy. Mol Ther Methods Clin Dev (2016) 0.95
Isolation and characterization of a Chinese hamster ovary mutant cell line with altered sensitivity to vaccinia virus killing. J Virol (1996) 0.95
Construction and use of a dominant, selectable marker: a Harvey sarcoma virus-dihydrofolate reductase chimera. Mol Cell Biol (1983) 0.95
Capture of a cellular transcriptional unit by a retrovirus: mode of provirus activation in embryonal carcinoma cells. J Virol (1992) 0.94
Amplification and expression of human alpha-globin genes in Chinese hamster ovary cells. Mol Cell Biol (1984) 0.94
Characterization of unintegrated retroviral DNA with long terminal repeat-associated cell-derived inserts. J Virol (1992) 0.93
Genetic background affects integration frequency of ecotropic proviral sequences into the mouse germ line. J Virol (1986) 0.93
Rearrangements of chicken immunoglobulin genes in lymphoid cells transformed by the avian retroviral oncogene v-rel. Proc Natl Acad Sci U S A (1988) 0.93
Determination of the frequency of retroviral recombination between two identical sequences within a provirus. J Virol (2000) 0.91
Isolation of a retroviruslike sequence from the TL locus of the C57BL/10 murine major histocompatibility complex. J Virol (1986) 0.90
Alteration of the tumorigenic and metastatic properties of neoplastic cells is associated with the process of calcium phosphate-mediated DNA transfection. Proc Natl Acad Sci U S A (1987) 0.90
Recombination between two integrated proviruses, one of which was inserted near c-myc in a retrovirus-induced rat thymoma: implications for tumor progression. J Virol (1988) 0.90
Genetic instability at the adenine phosphoribosyltransferase locus in mouse L cells. Mol Cell Biol (1982) 0.89
Genetically modified T cells for the treatment of malignant disease. Transfus Med Hemother (2013) 0.87
Characterization of a retrovirus shuttle vector capable of either proviral integration or extrachromosomal replication in mouse cells. Mol Cell Biol (1985) 0.87
Effect of proviral insertion on transcription of the murine B2mb gene. J Virol (1989) 0.87
Tsp transposons: a heterogeneous family of mobile sequences in the genome of the sea urchin Strongylocentrotus purpuratus. Mol Cell Biol (1985) 0.87
Human adenovirus type 2 but not adenovirus type 12 is mutagenic at the hypoxanthine phosphoribosyltransferase locus of cloned rat liver epithelial cells. J Virol (1983) 0.85
Herpes simplex virus type 2 mutagenesis: characterization of mutants induced at the hprt locus of nonpermissive XC cells. Mol Cell Biol (1986) 0.84
Loss of heterozygosity at the Ink4a/Arf locus facilitates Abelson virus transformation of pre-B cells. J Virol (2000) 0.82
The lethal yellow allele-associated provirus results in the production of chimeric viral-host RNAs. Proc Natl Acad Sci U S A (1987) 0.79
DNA methylation of helper virus increases genetic instability of retroviral vector producer cells. J Virol (2000) 0.78
Plasmid mediated mutagenesis of a cellular gene in transfected eukaryotic cells. Nucleic Acids Res (1987) 0.78
Endogenous retroviruses lead to the expression of a histocompatibility antigen detectable by skin graft rejection. Proc Natl Acad Sci U S A (1987) 0.77
Functional in vitro assays for the isolation of cell transformation effector and suppressor genes. Environ Health Perspect (1991) 0.76
Expression of an 86-kilodalton glycoprotein in an idiopathic mammary adenocarcinoma of a BALB/c mouse. Proc Natl Acad Sci U S A (1984) 0.75
Lessons Learned from Mouse Mammary Tumor Virus in Animal Models. ILAR J (2016) 0.75
A novel styryl diphenylamine derivative reverts the transformed phenotype of human fibrosarcoma HT1080 cells. Br J Cancer (1995) 0.75
Mapping unintegrated avian sarcoma virus DNA: termini of linear DNA bear 300 nucleotides present once or twice in two species of circular DNA. Cell (1978) 13.33
The molecular biology of the hepatitis B viruses. Annu Rev Biochem (1987) 12.32
Evidence that the transforming gene of avian sarcoma virus encodes a protein kinase associated with a phosphoprotein. Cell (1978) 11.17
Correct integration of retroviral DNA in vitro. Cell (1987) 10.73
Characterization of ribosomal frameshifting in HIV-1 gag-pol expression. Nature (1988) 10.69
DNA related to the transforming gene(s) of avian sarcoma viruses is present in normal avian DNA. Nature (1976) 9.81
Amplification of N-myc in untreated human neuroblastomas correlates with advanced disease stage. Science (1984) 9.64
Many tumors induced by the mouse mammary tumor virus contain a provirus integrated in the same region of the host genome. Cell (1982) 9.29
Multiple arrangements of viral DNA and an activated host oncogene in bursal lymphomas. Nature (1982) 9.12
Form and function of retroviral proviruses. Science (1982) 8.80
A nucleoprotein complex mediates the integration of retroviral DNA. Genes Dev (1989) 8.80
Amplified DNA with limited homology to myc cellular oncogene is shared by human neuroblastoma cell lines and a neuroblastoma tumour. Nature (1983) 8.18
Retroviral integration: structure of the initial covalent product and its precursor, and a role for the viral IN protein. Proc Natl Acad Sci U S A (1989) 8.13
Uninfected vertebrate cells contain a protein that is closely related to the product of the avian sarcoma virus transforming gene (src). Proc Natl Acad Sci U S A (1979) 7.55
Proviruses of avian sarcoma virus are terminally redundant, co-extensive with unintegrated linear DNA and integrated at many sites. Cell (1978) 7.46
Molecular cloning and characterization of avian sarcoma virus circular DNA molecules. J Virol (1980) 7.37
Signals for ribosomal frameshifting in the Rous sarcoma virus gag-pol region. Cell (1988) 7.14
Homogeneously staining chromosomal regions contain amplified copies of an abundantly expressed cellular oncogene (c-myc) in malignant neuroendocrine cells from a human colon carcinoma. Proc Natl Acad Sci U S A (1983) 7.01
Analysis of avian leukosis virus DNA and RNA in bursal tumours: viral gene expression is not required for maintenance of the tumor state. Cell (1981) 6.98
Expression of the int-1 gene in transgenic mice is associated with mammary gland hyperplasia and adenocarcinomas in male and female mice. Cell (1988) 6.48
Structure and variability of human chromosome ends. Mol Cell Biol (1990) 6.18
Expression of the Rous sarcoma virus pol gene by ribosomal frameshifting. Science (1985) 5.90
A mutant murine leukemia virus with a single missense codon in pol is defective in a function affecting integration. Proc Natl Acad Sci U S A (1984) 5.81
The molecular genetics of cellular oncogenes. Annu Rev Genet (1984) 5.72
Polymerase gene products of hepatitis B viruses are required for genomic RNA packaging as wel as for reverse transcription. Nature (1990) 5.68
Induction and apoptotic regression of lung adenocarcinomas by regulation of a K-Ras transgene in the presence and absence of tumor suppressor genes. Genes Dev (2001) 5.67
The size and genetic composition of virus-specific RNAs in the cytoplasm of cells producing avian sarcoma-leukosis viruses. Cell (1977) 5.23
Nucleotide sequence of an avian sarcoma virus oncogene (src) and proposed amino acid sequence for gene product. Nature (1980) 5.22
Purification of DNA complementary to nucleotide sequences required for neoplastic transformation of fibroblasts by avian sarcoma viruses. J Mol Biol (1976) 5.07
A receptor for subgroup A Rous sarcoma virus is related to the low density lipoprotein receptor. Cell (1993) 4.97
The low molecular weight RNAs of Rous sarcoma virus. I. The 4 S RNA. Virology (1970) 4.64
Virus-specific DNA in the cytoplasm of avian sarcoma virus-infected cells is a precursor to covalently closed circular viral DNA in the nucleus. J Virol (1978) 4.55
Wnt genes. Cell (1992) 4.55
Location and function of retroviral and SV40 sequences that enhance biochemical transformation after microinjection of DNA. Cell (1983) 4.53
Nucleotide sequences related to the transforming gene of avian sarcoma virus are present in DNA of uninfected vertebrates. Proc Natl Acad Sci U S A (1978) 4.47
Nucleotide sequences at host-proviral junctions for mouse mammary tumour virus. Nature (1981) 4.38
Human N-myc gene contributes to neoplastic transformation of mammalian cells in culture. Nature (1985) 4.31
Integration of deoxyribonucleic acid specific for Rous sarcoma virus after infection of permissive and nonpermissive hosts. Proc Natl Acad Sci U S A (1973) 4.19
A joint produce of the genes gag and pol of avian sarcoma virus: a possible precursor of reverse transcriptase. Cell (1977) 4.18
Glycogen synthase kinase-3 and dorsoventral patterning in Xenopus embryos. Nature (1995) 4.14
Biochemical and genetic evidence for the hepatitis B virus replication strategy. Science (1986) 4.12
Cellular functions are required for the synthesis and integration of avian sarcoma virus-specific DNA. Cell (1977) 4.06
Kinetics of synthesis, structure and purification of avian sarcoma virus-specific DNA made in the cytoplasm of acutely infected cells. J Mol Biol (1978) 4.04
Information access. Building a "GenBank" of the published literature. Science (2001) 3.95
The purified product of the transforming gene of avian sarcoma virus phosphorylates tyrosine. J Biol Chem (1980) 3.95
Nucleotide sequence of an infectious molecularly cloned genome of ground squirrel hepatitis virus. J Virol (1984) 3.91
Regulation of inducible enzyme synthesis in Escherichia coli by cyclic adenosine 3', 5'-monophosphate. J Biol Chem (1969) 3.86
Two efficient ribosomal frameshifting events are required for synthesis of mouse mammary tumor virus gag-related polyproteins. Proc Natl Acad Sci U S A (1987) 3.84
Nucleotide sequence of cloned unintegrated avian sarcoma virus DNA: viral DNA contains direct and inverted repeats similar to those in transposable elements. Proc Natl Acad Sci U S A (1981) 3.82
A constitutively active epidermal growth factor receptor cooperates with disruption of G1 cell-cycle arrest pathways to induce glioma-like lesions in mice. Genes Dev (1998) 3.68
Ethidium bromide inhibits appearance of closed circular viral DNA and integration of virus-specific DNA in duck cells infected by avian sarcoma virus. Nature (1975) 3.63
Integration of the DNA of mouse mammary tumor virus in virus-infected normal and neoplastic tissue of the mouse. Cell (1979) 3.63
Nucleosomes, DNA-binding proteins, and DNA sequence modulate retroviral integration target site selection. Cell (1992) 3.60
Genetic lesion in homozygous alpha thalassaemia (hydrops fetalis). Nature (1974) 3.58
A cellular oncogene (c-Ki-ras) is amplified, overexpressed, and located within karyotypic abnormalities in mouse adrenocortical tumour cells. Nature (1983) 3.56
Isolation of a chicken gene that confers susceptibility to infection by subgroup A avian leukosis and sarcoma viruses. J Virol (1993) 3.46
Mapping of linear and circular forms of mouse mammary tumor virus DNA with restriction endonucleases: evidence for a large specific deletion occurring at high frequency during circularization. Proc Natl Acad Sci U S A (1978) 3.45
Dexamethasone-mediated induction of mouse mammary tumor virus RNA: a system for studying glucocorticoid action. Cell (1975) 3.44
Corrections to the nucleotide sequence of the src gene of Rous sarcoma virus. Nature (1983) 3.42
Transduction of a cellular oncogene: the genesis of Rous sarcoma virus. Proc Natl Acad Sci U S A (1983) 3.41
Production of mouse mammary tumor virus by cultured cells in the absence and presence of hormones: assay by molecular hybridization. Virology (1975) 3.40
Two proto-oncogenes implicated in mammary carcinogenesis, int-1 and int-2, are independently regulated during mouse development. Proc Natl Acad Sci U S A (1986) 3.34
Glucocorticoid-stimulated accumulation of mouse mammary tumor virus RNA: increased rate of synthesis of viral RNA. Proc Natl Acad Sci U S A (1977) 3.31
Transcription of the hepatitis B surface antigen gene in cultured murine cells initiates within the presurface region. J Virol (1984) 3.30
Detection of avian tumor virus-specific nucleotide sequences in avian cell DNAs (reassociation kinetics-RNA tumor viruses-gas antigen-Rous sarcoma virus, chick cells). Proc Natl Acad Sci U S A (1972) 3.28
Regulation of lac mRNA synthesis in a soluble cell-free system. Nat New Biol (1971) 3.25
The first seven amino acids encoded by the v-src oncogene act as a myristylation signal: lysine 7 is a critical determinant. Mol Cell Biol (1988) 3.24
Appearance of virus-specific DNA in mammalian cells following transformation by Rous sarcoma virus. J Mol Biol (1973) 3.21
Proposal for naming host cell-derived inserts in retrovirus genomes. J Virol (1981) 3.18
The nucleotide sequence of an untranslated but conserved domain at the 3' end of the avian sarcoma virus genome. Nucleic Acids Res (1980) 3.16
Endogenous mammary tumour virus DNA varies among wild mice and segregates during inbreeding. Nature (1979) 3.15
Regulation of Wnt signaling by Sox proteins: XSox17 alpha/beta and XSox3 physically interact with beta-catenin. Mol Cell (1999) 3.15
Biosynthesis of the reverse transcriptase of hepatitis B viruses involves de novo translational initiation not ribosomal frameshifting. Nature (1989) 3.10
Expression of v-src and chicken c-src in rat cells demonstrates qualitative differences between pp60v-src and pp60c-src. Cell (1984) 3.06
Inhibition of secretion of hepatitis B surface antigen by a related presurface polypeptide. Science (1986) 3.01
RNA-directed DNA synthesis by virions of Rous sarcoma virus: further characterization of the templates and the extent of their transcription. Virology (1973) 3.00
Basic fibroblast growth factor induces cell migration and proliferation after glia-specific gene transfer in mice. Proc Natl Acad Sci U S A (1998) 3.00
Characteristics of virus-specific RNA in avian sarcoma virus-transformed BHK-21 cells and revertants. Virology (1977) 2.99
DNA polymerases of Rous sarcoma virus: delineation of two reactions with actinomycin. Nature (1970) 2.93
Deoxyribonucleic acid polymerase associated with Rous sarcoma virus and avian myeloblastosis virus: properties of the enzyme and its product. J Virol (1970) 2.86
Retroviral integration into minichromosomes in vitro. EMBO J (1992) 2.85
Human immunodeficiency virus type 1 integrase mutants retain in vitro integrase activity yet fail to integrate viral DNA efficiently during infection. J Virol (1996) 2.82
Synthesis, structure and function of avian sarcoma virus-specific DNA in permissive and nonpermissive cells. Cold Spring Harb Symp Quant Biol (1975) 2.79
A small region of the mouse mammary tumor virus long terminal repeat confers glucocorticoid hormone regulation on a linked heterologous gene. Proc Natl Acad Sci U S A (1983) 2.79
c-Src enhances the spreading of src-/- fibroblasts on fibronectin by a kinase-independent mechanism. Genes Dev (1995) 2.72
Ultrasonography and computed tomography reduce unnecessary surgery in abdominal rectus sheath haematoma. Br J Surg (1997) 2.71
Site-directed mutagenesis of HIV-1 integrase demonstrates differential effects on integrase functions in vitro. J Biol Chem (1993) 2.69
Identification of a human gene (HCK) that encodes a protein-tyrosine kinase and is expressed in hemopoietic cells. Mol Cell Biol (1987) 2.59
An RNA pseudoknot and an optimal heptameric shift site are required for highly efficient ribosomal frameshifting on a retroviral messenger RNA. Proc Natl Acad Sci U S A (1992) 2.57
Use of MMTV-Wnt-1 transgenic mice for studying the genetic basis of breast cancer. Oncogene (2000) 2.56
Heterogeneity of genetic loci in chickens: analysis of endogenous viral and nonviral genes by cleavage of DNA with restriction endonucleases. Cell (1979) 2.55
5'-terminal sequences influence the segregation of ground squirrel hepatitis virus RNAs into polyribosomes and viral core particles. J Virol (1987) 2.54
Nucleotide sequence of the 5' noncoding region and part of the gag gene of Rous sarcoma virus. J Virol (1982) 2.53
The leader sequence of the subgenomic mRNA's of Rous sarcoma virus is approximately 390 nucleotides. J Virol (1982) 2.51
Characteristics of cellular RNA related to the transforming gene of avian sarcoma viruses. Cell (1978) 2.50
The preS1 protein of hepatitis B virus is acylated at its amino terminus with myristic acid. J Virol (1987) 2.49
Human immunodeficiency virus type 1 gag-pol frameshifting is dependent on downstream mRNA secondary structure: demonstration by expression in vivo. J Virol (1992) 2.49
DNA bending creates favored sites for retroviral integration: an explanation for preferred insertion sites in nucleosomes. EMBO J (1994) 2.48