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Biomedical subjects

S McGavin

Publications and source records attributed to S McGavin.

17 recordsLinked to original sources
PubMed1989

Four strand recombination models.

A main point of this paper is to develop the idea that synapsis of DNA duplexes might take place by Watson-Crick base pairing between essentially intact duplex structure to form a four stranded intermediate. This intermediate is the same regular and compact four strand structure already discussed (e.g., McGavin, 1971a, J. molec. Biol., 55, 293-298; 1979, J. theor. Biol., 77, 83-99) and which has been used in several related recombination models (see, for example, McGavin, 1977, Heredity, 39, 15-25; 1984, J. theor. Biol., 107, 37-56; Wilson, 1979, Proc. natn. Acad. Sci. U.S.A., 76, 3641-3645; Nash et al., 1980, Cold Spring Harbor Symposium of Quantitative Biology, 45, 417-428; Nash, 1981, A. Rev. Genetics, 15, 143-167). These models can also be related to one recently suggested by Hopkins (1986, J. theor. Biol. 120, 215-222). An immediate stimulus to the development of the idea was the recent work of Griffith & Nash (1985, Proc. natn. Acad. Sci. U.S.A., 82, 3124-3128), on the site specific recombination system of the lambda bacteriophage. They observed trefoil knots with exclusively positive nodes among the products of the interaction of two relatively inverted attachment sites within circular molecules. The model discussed here may though be of interest in itself. The paper also compares several closely related models for recombination which involve formation of either identical or closely related four strand secondary structures.

DNA↗
PubMed1989

A computer graphics study of multistranded DNA models.

A range of related nucleic acid models has been built using the computer graphics system at EMBL (Heidelberg). The relationship between these models is considered in terms of a simple "core" structure. One of these models is a four-strand structure in which two duplexes of the Watson-Crick kind are specifically related by a twofold rotation axis and which has already been discussed in some detail. The models fall into two principal classes. In one, each sugar phosphate chain is attached to every layer of bases in the "core" structure; in the other, each chain is attached to alternate layers of bases. Several of the models discussed have specificity both of complementarity and of identity.

Computer Graphics↗
PubMed1986

A simple and effective technique for increasing pregnancy rates in couples with retrograde ejaculation.

Seven of 12 patients with retrograde ejaculation, who had at least occasional samples with reasonable sperm numbers and motility, underwent a protocol including luteinizing hormone-timed, intrauterine insemination with washed sperm recovered from the urine. Seven pregnancies have occurred to date in six patients; the one other patient is still early in the protocol period. The described technique for collecting sperm, ovulation timing, sperm recovery, and washing and intrauterine insemination are relatively simple and cost-effective and appear to be effective in contributing to pregnancies in many couples with retrograde ejaculation.

Ejaculation↗
PubMed1984

Construction and use of models designed to demonstrate some topological properties of multistranded nucleic acid structure and its possible bearing on recombination.

A description is given of the construction and use of a simple model designed to show the consequences of association between duplexes to form some kind of four strand structure in recombination. The model was first devised to help in consideration of the work of Nash et al. (1980). Conclusions drawn from it may however be of wider interest. The model was designed with a detailed molecular model in mind (McGavin, 1971a, 1979). It could however apply to any close juxtaposition of duplexes. A close juxtaposition of duplexes is a feature of several models for recombination, although this is not often referred to explicitly as four strand structure.

DNA↗
PubMed1977

A model for the specific pairing of homologous double-stranded nucleic acid molecules during genetic recombination.

A model involving a specific pairing of homologous double-stranded nucleic acid molecules is applied to some parts of genetic recombination. The most original features of this application of the model relate to the initiation process, a part of which can be described by a highly compact and symmetrical structure. The model also provides a simple view of the formation of hybrid nucleic acid. The possibilities of detecting four-strand structures are briefly discussed.

DNA↗