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Biomedical subjects

S Lien

Publications and source records attributed to S Lien.

71 records · Page 4Linked to original sources
PubMed1972

Biochemical physiology of a respiration-deficient mutant of the photosynthetic bacterium Rhodopseudomonas capsulata.

Nonsulfur purple photosynthetic bacteria generally possess the adaptive capacity to grow anaerobically (photosynthetically) and aerobically in darkness (energy obtained by respiratory phosphorylation). To develop a test system for study of interactions between the photosynthetic energy-conversion and dark respiration systems and the mechanism by which O(2) inhibits bacteriochlorophyll synthesis, we have isolated a mutant of Rhodopseudomonas capsulata that is incapable of dark aerobic growth. Both the parent strain and the mutant strain Z-1 (aer-13) grow readily anaerobically in the light with either malate or succinate as the source of carbon and reducing power. They differ, however, in that membrane fragments ("chromatophores") from the mutant show severely impaired ability to use reduced nicotinamideadenine dinucleotide (NADH) as a source of electrons for respiration, oxidative phosphorylation, or "redox buffering" of the photophosphorylation system. The results presented indicate that the genetic lesion responsible for greatly diminished capacity to oxidize NADH can account for inability of Rps. capsulata Z-1 (aer-13) to grow aerobically in darkness.

Aerobiosis↗
PubMed1971

Mutational and physiological enhancement of photosynthetic energy conversion in Rhodopseudomonas capsulata.

Photosynthetic growth of Rhodopseudomonas capsulata, a nonsulfur purple bacterium, is severely inhibited by inorganic arsenate when this anion is present equimolar to orthophosphate in the culture medium. Studies on an arsenate-resistant mutant indicate that its resistance can be explained by a significantly increased photophosphorylation capacity of the energy-converting machinery, which can compensate for the decrease in adenosine triphosphate regeneration rate caused by esterification of arsenate in place of phosphate. Repeated subculture of the mutant in the presence of arsenate, under certain conditions, yields cell populations that have strikingly elevated contents of membrane-bound reaction-center bacteriochlorophyll, cytochromes, and photo-phosphorylation coupling factor. Membranes from such cells show unusually high photophosphorylation activity, and can be expected to provide a useful experimental material for more refined analysis of the mechanism of the energy-conversion process.

Adenosine Triphosphate↗
PubMedDate not supplied

Direct estimation of the recombination frequency between the RB1 gene and two closely linked microsatellites using sperm typing.

In this study, single sperm typing has been used for high-resolution recombination analysis between the retinoblastoma gene and two closely linked extragenic microsatellites (D13S284 and D13S1307). The analysis of 1198 single sperm from three donors allowed the determination of recombination fractions between RB1.20 and D13S284 and RB1.20 and D13S1307 of 0.022 and 0.033, respectively. These results show that RB1 gene and the two microsatellites are closely linked, which validates their potential use in indirect genetic diagnosis of retinoblastoma.

Genetic Linkage↗
PubMedDate not supplied

Genetic diversity and population structure of 20 North European cattle breeds.

Blood samples were collected from 743 animals from 15 indigenous, 2 old imported, and 3 commercial North European cattle breeds. The samples were analyzed for 11 erythrocyte antigen systems, 8 proteins, and 10 microsatellites, and used to assess inter- and intrabreed genetic variation and genetic population structures. The microsatellites BoLA-DRBP1 and CSSM66 were nonneutral markers according to the Ewens-Watterson test, suggesting some kind of selection imposed on these loci. North European cattle breeds displayed generally similar levels of multilocus heterozygosity and allelic diversity. However, allelic diversity has been reduced in several breeds, which was explained by limited effective population sizes over the course of man-directed breed development and demographic bottlenecks of indigenous breeds. A tree showing genetic relationships between breeds was constructed from a matrix of random drift-based genetic distance estimates. The breeds were classified on the basis of the tree topology into four major breed groups, defined as Northern indigenous breeds, Southern breeds, Ayrshire and Friesian breeds, and Jersey. Grouping of Nordic breeds was supported by documented breed history and geographical divisions of native breeding regions of indigenous cattle. Divergence estimates between Icelandic cattle and indigenous breeds suggested a separation time of more than 1,000 years between Icelandic cattle and Norwegian native breeds, a finding consistent with historical evidence.

Alleles↗
PubMedDate not supplied

Frequencies of genes for coat colour and horns in Nordic cattle breeds.

Gene frequencies of coat colour and horn types were assessed in 22 Nordic cattle breeds in a project aimed at establishing genetic profiles of the breeds under study. The coat colour loci yielding information on genetic variation were: extension, agouti, spotting, brindle, dun dilution and colour sided. The polled locus was assessed for two alleles. A profound variation between breeds was observed in the frequencies of both colour and horn alleles, with the older breeds generally showing greater variation in observed colour, horn types and segregating alleles than the modern breeds. The correspondence between the present genetic distance matrix and previous molecular marker distance matrices was low (r = 0.08 - 0.12). The branching pattern of a neighbour-joining tree disagreed to some extent with the molecular data structure. The current data indicates that 70% of the total genetic variation could be explained by differences between the breeds, suggesting a much greater breed differentiation than typically found at protein and microsatellite loci. The marked differentiation of the cattle breeds and observed disagreements with the results from the previous molecular data in the topology of the phylogenetic trees are most likely a result of selection on phenotypic characters analysed in this study.

Journal Article↗