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Biomedical subjects

H M Dodd

Publications and source records attributed to H M Dodd.

24 records · Page 2Linked to original sources
PubMed1990

Analysis of the genetic determinant for production of the peptide antibiotic nisin.

The structural gene for the precursor of the peptide antibiotic nisin was isolated and characterized. As with other lanthionine-containing antibiotics, nisin is synthesized as a pre-propeptide which undergoes post-translational modification to generate the mature antibiotic. The sequence data obtained agreed with those of precursor nisin genes isolated by other workers from different Lactococcus lactis strains. Analysis of regions flanking the precursor nisin gene revealed the presence of a downstream open reading frame that may be involved in maturation of the precursor molecule. Nucleotide sequences characteristic of an IS element were located upstream of the nisin determinant. This element, termed IS904, is present in multiple copies in the genome of L. lactis. The nisin determinant of L. lactis is a component of a large transmissible gene block that also encodes nisin resistance and sucrose-metabolizing genes. Gene probe experiments indicated that the nisin/sucrose gene block was located in the chromosome. Furthermore, the copy of IS904 identified adjacent to the precursor nisin gene lies at, or very close to, one end of this transmissible DNA segment and may play a role in mediating its transfer between strains.

Amino Acid Sequence↗
PubMed1987

The R46 site-specific recombination system is a homologue of the Tn3 and gamma delta (Tn1000) cointegrate resolution system.

The nucleotide sequence of the R46 site-specific recombination system has been determined. The organization of the recombination gene (perR46) and the site at which it acts (per site), together with the extensive sequence homology displayed with the tnpR genes and res sites of the transposons Tn3 and gamma delta (Tn1000), suggests that they have been derived from a Tn3-like element. These site-specific recombination functions of R46 play a role in plasmid maintenance.

Base Sequence↗
PubMed1986

Evolution of R plasmids by replicon fusion.

The occurrence of plasmid-plasmid fusions in nature and their possible influence on the spread of bacterial drug resistance is considered. Three ways in which replicon fusions can be formed are described; specifically fusions mediated by IS elements, "one-ended transposition" systems derived from Tn3 and like transposons, and pUB2380, a prototype for a new type of transposition. Non-transposition based systems which mediate replicon fusion are also briefly considered.

Biological Evolution↗
PubMed1986

Location of the site-specific recombination system of R46: a function necessary for plasmid maintenance.

The R46 site-specific recombination system comprises a per (plasmid-encoded recombinase) gene and a site at which the gene product acts, the per site. The two functions have been cloned into pACYC184. They are encoded by sequences within a region of approximately 2 kb on the R46 genome. These R46 sequences are closely related to the site-specific recombination systems of the ampicillin resistance transposons collectively designated TnA. The R46 per function is interchangeable with the tnpR gene product of TnA. Both enzymes can mediate recombination between the related res and per sites in R46::TnA recombinant plasmids to generate site-specific deletions and inversions. Similar DNA rearrangements occur when TnA inserts into pACYC184 derivatives carrying the cloned R46 per functions. Carriage of this site-specific recombination system contributes to the stable maintenance of R46. By converting plasmid dimers to monomers the R46 per functions help to ensure equal partitioning at cell division.

Cloning, Molecular↗
PubMed1983

R46 encodes a site-specific recombination system interchangeable with the resolution function of TnA.

Transposition of Tn4 onto the IncN plasmic R46 generates unstable DNA molecules. The R46::TnA recombinant plasmids undergo further DNA rearrangements which depend on the orientation in which the TnA element is inserted into the plasmid, and deletions and inversions of R46 and TnA sequences have been observed. Both types of rearrangement have the same specific endpoints, one within TnA and one located between the R46 coordinates, 36.0 and 37.0. The results are consistent with the operation of a recA-independent, site-specific recombination system utilizing, at least in part, the transposon cointegrate resolution system of TnA, together with R46-encoded functions. Data are presented that indicate that R46 encodes analogs of both the res site of TnA and its tnpR gene, although little homology between this element and the plasmid is apparent. Models for the TnA-induced generation of site-specific deletions and inversions upon transposition of TnA to R46 are presented.

Chromosome Deletion↗