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M H Edgell

Publications and source records attributed to M H Edgell.

At least 19 recordsLinked to original sources
PubMed1992

Strand-specific LINE-1 transcription in mouse F9 cells originates from the youngest phylogenetic subgroup of LINE-1 elements.

LINE-1 (L1) is a mammalian family of highly repeated DNA sequences that are members of a class of transposable elements whose movement involves an RNA intermediate. Both structural and evolutionary data indicate that the L1 family consists of a small number of active transposable elements interspersed with a large number of L1 pseudogenes. In the mouse, the longest, characterized L1 sequences span about 7000 base-pairs and contain two long open reading frames. Two subfamilies of mouse L1 elements, A and F, have been defined on the basis of the type of putative transcriptional regulatory sequence found at the 5' end. In order to identify a transcribed subset of L1 elements in mouse F9 teratocarcinoma cells, we have examined the strand-specificity of L1 transcription by Northern analysis and compared the open reading frame-1 sequences of ten A-type cDNAs with fifteen genomic A-type L1 elements. Transcripts containing A-type sequence are far more abundant than those containing F-type sequence. Although the majority of L1 RNA in F9 cells appears to be transcribed non-specifically from both strands, our results provide evidence for a subpopulation of variable length, strand-specific transcripts arising from A-type transcriptional regulatory sequences. F9 cell cDNA sequences, which share greater than 99.5% sequence identity with one another, represent a homogeneous subset of the genomic L1 population. Examination of genomic mouse L1 sequences reveals three types of length polymorphism in a defined segment of the first open reading frame. Phylogenetic analysis shows a correlation between the type of length polymorphism in the first open reading frame and the relative age of an individual A-type genomic L1 element. Comparison of the cDNA and genomic sequences indicates that the youngest subgroup of A-type L1 elements is preferentially transcribed in F9 cells. This subgroup may be currently dominating the L1 dispersal process in mice.

Amino Acid Sequence↗
PubMed1992

Identification of transcriptional regulatory activity within the 5' A-type monomer sequence of the mouse LINE-1 retroposon.

LINE-1 (L1) is a retroposon found in all mammals. In the mouse, approximately 10% of L1 elements are full-length and can be grouped into two classes, A or F, based upon the type of monomer sequence repeated at the 5' end. In order to test for promoter activity in the 5' end of the A-type mouse L1 element, we cloned several different A-monomers into a promoterless chloramphenicol acetyltransferase (CAT) vector. The A-monomer constructs varied in their ability to regulate transcription of the CAT gene, exhibiting CAT activity 16-37% of that detected with the Rous sarcoma virus promoter and enhancer. A series of A-monomer deletions were tested for their ability to regulate CAT expression and gel retardation experiments were performed to identify regions of the A-monomer that may be involved in L1 transcriptional regulation. A-monomer sequences are usually found repeated 2-5 times at the 5' end of a full-length mouse L1. In the absence of long terminal repeats or an internal promoter, the tandem array of A-monomers may provide a mechanism for A-type L1 elements to generate transcripts containing transcriptional regulatory sequences.

Animals↗
PubMed1992

Master genes in mammalian repetitive DNA amplification.

The analysis of species-specific subfamilies of both the LINE and SINE mammalian repetitive DNA families suggests that such subfamilies have arisen by amplification of an extremely small group of 'master' genes. In contrast to the master genes, the vast majority of both SINEs and LINEs appear to behave like psudogenes in their inability to undergo extensive amplification.

Animals↗
PubMed1991

Composite of A and F-type 5' terminal sequences defines a subfamily of mouse LINE-1 elements.

The 5' terminus of full-length L1 elements contains transcriptional control sequences. In mouse L1 (L1Md) elements, these sequences exist as an array of tandem direct repeats. Two types of repeat units, termed A-monomers and F-monomers, have been reported. Both monomers are about 200 bp in length but share no significant sequence homology. Previous studies have identified L1Md elements containing either A or F-monomers but not both. Here we describe three "composite" L1Md elements that contain both types of monomer sequence. Two of these composite L1Md elements are highly homologous and share the same structural rearrangements, implying that they arose from a common ancestor that has the same composite 5' end.

Animals↗
PubMed1991

L1 gene conversion or same-site transposition.

DNA sequence analysis of the same chromosomal region from two haplotypes of Mus musculus and from the related species M. caroli and M. pahari reveals the presence of long interspersed sequence one (LINES-1, or L1) elements residing at the same nucleotide position in the two most distantly related of the species (M. musculus and M. pahari). The DNA sequence of each of these L1 elements is more similar to that of other L1 elements from its own species than to the other. Thus, the L1 sequence at each of these sites is recent with respect to the divergence of the species. This could be a result of recent gene conversion of L1 elements inherited from a common ancestor or of two recent independent L1 insertion events at the same nucleotide position in the two species. Such specificity of insertion would be quite different from the apparent randomness of other characterized L1 insertion events, such as those in the beta-globin locus. If the recent L1 sequences arose at this site by gene conversion of an ancestral L1 element, then the absence of an L1 element at this location in the M. caroli chromosome examined could arise either from its precise deletion from M. caroli or from the segregation into M. caroli of a polymorphic chromosome present in the ancestral population which was missing this L1 element.

Animals↗
PubMed1979

DNA fragments of the Mus musculus beta globin haplotypes Hbbs and Hbbd.

Two alternative haplotypes at the complex locus controlling hemoglobin beta chain synthesis in Mus musculus were compared at the DNA level. As expected, Hbbd homozygotes--which as adults synthesize two species of beta chain--have two genes for beta globin. Adult mice homozygous for the Hbbs haplotype make only a single type of beta polypeptide, yet they also have two beta globin genes. Apparently the two Hbbs genes encode identical proteins, or one of the two genes is not detectably expressed. The Hbbs and Hbbd haplotypes are thus more similar at the DNA level than studies of their polypeptide products have indicated.

Animals↗
PubMed1978

Mutagenesis at a specific position in a DNA sequence.

Predefined changes in a known DNA sequence were introduced by a general method. Oligodeoxyribonucleotides complementary to positions 582 to 593 of the viral DNA strand of the bacteriophage phiX174 am3 mutant (pGTATCCTACAAA), and to the wild type sequence in this region (pGTATCCTACAAA), were synthesized and used as specific mutagens. Each of these oligonucleotides was incorporated into a complete circular complementary strand when used as primer on a genetically heterologous viral strand template, by the combined action of subtilisin-treated Escherichia coli DNA polymerase I and T4 DNA ligase. Incomplete duplexes were removed or were inactivated by nuclease S1 and the products were used to transfect spheroplasts of E. coli. Both oligonucleotides induced specific mutations at high efficiency when used with heterologous template (15% mutants among progeny phage). The am phages isolated by this procedure are phenotypically gene E mutants, and contain A at position 587 of the viral strand. They thus appear identical with am3 and provide evidence that the change G leads to A at position 587 is sufficient to produce a defective E function. Since the template for the induction of am mutants carried another genetic marker (sB1), the strains carrying the induced mutations have the new genotype am3 sB1. It should be possible to introduce the am3 mutation into any known mutant strain of phi174 using this same oligonucleotide. Both possible transition mutations were induced in these experiments. In principle, the method could also induce transversions, insertions, and deletions. The method should be applicable to other circular DNAs of similar size, for example recombinant DNA plasmids.

Base Sequence↗
PubMed1978

A comparison of two cloned mouse beta-globin genes and their surrounding and intervening sequences.

The BALC/c mouse has two nonallelic beta-globin genes that appear to reside on two different Eco R1 fragments of genomic DNA. We have already cloned one of these fragments and shown that the gene encoded within it is interrupted by at least one large intervening sequence of DNA. We have now cloned and characterized the second beta-globin gene-containing fragment. The coding sequence of its gene is also interrupted by an intervening sequence of DNA that occurs in about the same position, relative to the coding sequence, as does the first. Because some shared features of the structure of these two genes might be responsible for their coordinate expression and the elimination of their intervening sequences, we have compared their surrounding, coding and intervening sequences by restriction endonuclease analysis and by visualization of the heteroduplex structures formed between them. Of the 7000 bp of sequence compared in this way, we find only a few hundred base pairs of homology in addition to the coding sequence. These shared sequences flank the coding sequence and appear to include only those portions of the intervening sequence immediately adjacent to the interrupted structural gene.

Animals↗
PubMed1978

Recognition site of Escherichia coli B restriction enzyme on phi XsB1 and simian virus 40 DNAs: an interrupted sequence.

Methyl groups placed on varphiXsB1 replicative form DNA by the Escherichia coli B modification enzyme are located in the overlap between fragments Mbo II-3 and Alu I-2, a 61-base-pair DNA segment. Mutations that led to loss of susceptibility to restriction by E. coli B occurred within this segment at three positions spanning 14 nucleotides. A sequence difference between varphiXsB1 and varphiXam3cs70, a varphiX174 strain not restricted by E. coli B, occurs at one of these positions. The site on simian virus 40 DNA methylated by the modification enzyme is located in the 115-base-pair overlap between fragments Hae III-I and Alu I-G. The sequences of these segments of varphiXsB1 and simian virus 40 DNA and two regions of phage f1 DNA recognized by the E. coli B restriction enzyme [Ravetch, J. V., Horiuchi, K. & Zinder, N. D. (1978) Proc. Natl. Acad. Sci. USA 75, 2266-2270] contain a homology of nine bases in the configuration:5'-T-G-A... 8N... T-G-C-T... 9N... T-N-N-T-3'. The sequence 5'-T-G-A... 8N... T-G-C-T-3' may constitute the restriction enzyme recognition site since it does not occur in varphiXam3cs70 DNA and occurs only once in simian virus 40 DNA, and since all observed mutations leading to loss of the site occur at one of the bases specified by this sequence. Analysis of the sequence of varphiXam3cs70 showed that if no other residues are recognized, all seven of these bases are essential for recognition and the interval between the two groups of specified bases must be precisely eight.

Base Sequence↗
PubMed1978

Multiple related immunoglobulin variable-region genes identified by cloning and sequence analysis.

We have identified at least six EcoRI fragments of mouse DNA that encode variable-region gene sequences closely related to the mouse kappa light chain, MOPC-149. Two of these fragments have been cloned, and the entire nucleotide sequence of the variable-region genes encoded on each has been determined. Both genes encode closely related variable-region sequences extending from codon position 1 through position 97. Neither fragment encodes a constant-region sequence. Although both genes are closely related, they differ from one another and from the sequence expressed in the MOPC-149 cell from which they were cloned. These few differences cluster within the complementarity-determining regions although several occur in framework sequences as well. We therefore conclude that an antibody-producing cell contains genetic information corresponding to its expressed sequence and several other closely related but silent sequences. These initial results raise the possibility that similar sets of genes might exist corresponding to each of the many subgroups already identified among mouse kappa light chains. If true, this would further suggest that the mouse genome might be rich enough in variable-region genes so as to encode a major portion of the variable-region repertoire.

Animals↗
PubMed1978

The ribosomal RNA gene region in the sea urchin Lytechinus variegatus.

A fine structure map of the ribosomal gene region of the sea urchin Lytechinus variegatus has been generated. The ribosomal DNA density satellite has been analyzed with restriction enzymes and by hybridization to urchin 18S and 26S ribosomal RNA (rRNA). The L. variegatus rRNA repeats show heterogeneity on the nontranscribed spacer. Minor bands containing transcribed spacer sequences are observed. One interpretation of these bands would require both transcribed spacer heterogeneity and defective ribosomal genes retained among the rRNA gene repeats.

Animals↗
PubMed1977

Isolation and characterization of the four major proteins in the virion of bacteriophage phiX174.

A preparative method is described for the isolation of the major protein species from the virion of bacteriophage phiX174. Two proteins, the cistron G and H products, are located in the virion spikes. After removal of the spikes, the capsid contains the cistron F product as well as a small protein which is the product of cistron J and the majority of the DNA. During the removal of the spikes, a precipitate containing the F and G proteins is formed. The proteins from the spike, capsid, or precipitate can be isolated on the basis of size by gel-filtration chromatography. The cistron G protein has an aminoterminal methionine, while the small J protein has an amino-terminal serine. Amino acid compositions as well as peptide maps indicate each species is unique and that, in sum, they account for over half the coding capacity of the viral genome.

Amino Acids↗