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161.
Chevonne D Eversley Tavia Clark Yuying Xie Jill Steigerwalt Timothy A Bell Fernando PM de Villena David W Threadgill 《BMC genetics》2010,11(1):1-6
Background
Sheep carcasses with yellow fat are sporadically observed at Norwegian slaughter houses. This phenomenon is known to be inherited as a recessive trait, and is caused by accumulation of carotenoids in adipose tissue. Two enzymes are known to be important in carotenoid degradation in mammals, and are therefore potential candidate genes for this trait. These are beta-carotene 15,15'-monooxygenase 1 (BCMO1) and the beta-carotene oxygenase 2 (BCO2).Results
In the present study the coding region of the BCMO1 and the BCO2 gene were sequenced in yellow fat individuals and compared to the corresponding sequences from control animals with white fat. In the yellow fat individuals a nonsense mutation was found in BCO2 nucleotide position 196 (c.196C>T), introducing a stop codon in amino acid position 66. The full length protein consists of 575 amino acids. In spite of a very low frequency of this mutation in the Norwegian AI-ram population, 16 out of 18 yellow fat lambs were found to be homozygous for this mutation.Conclusion
In the present study a nonsense mutation (c.196C>T) in the beta-carotene oxygenase 2 (BCO2) gene is found to strongly associate with the yellow fat phenotype in sheep. The existence of individuals lacking this mutation, but still demonstrating yellow fat, suggests that additional mutations may cause a similar phenotype in this population. The results demonstrate a quantitatively important role for BCO2 in carotenoid degradation, which might indicate a broad enzyme specificity for carotenoids. Animals homozygous for the mutation are not reported to suffer from any negative health or development traits, pointing towards a minor role of BCO2 in vitamin A formation. Genotyping AI rams for c.196C>T can now be actively used in selection against the yellow fat trait. 相似文献162.
MICHAEL A. WYDER LAURA Q. JOHNSTON EDNA S. KANESHIRO 《The Journal of eukaryotic microbiology》2010,57(5):447-448
ABSTRACT. Pneumocandins inhibit β‐1,3‐glucan synthesis preventing the development of Pneumocystis cysts that are absent from the lungs of treated rats. To determine whether treated trophozoites are capable of DNA replication, cytochemical analyses were performed on 4′,6‐diamidino‐2‐phenylindole (DAPI)‐ and DB181‐stained Pneumocystis carinii isolated from pneumocandin L‐693‐989‐treated rats. Fluorescence intensities of trophozoite nuclei from drug‐treated rats were greater than those of untreated controls, suggesting that DNA replication was not inhibited but that cytokinesis and perhaps karyokinesis were blocked. 相似文献
163.
E. PORCHER J. K. KELLY P.‐O. CHEPTOU C. G. ECKERT M. O. JOHNSTON S. KALISZ 《Journal of evolutionary biology》2009,22(4):708-717
The magnitude of inbreeding depression, a central parameter in the evolution of plant mating systems, can vary depending on environmental conditions. However, the underlying genetic mechanisms causing environmental fluctuations in inbreeding depression, and the consequences of this variation for the evolution of self‐fertilization, have been little studied. Here, we consider temporal fluctuations of the selection coefficient in an explicit genetic model of inbreeding depression. We show that substantial variance in inbreeding depression can be generated at equilibrium by fluctuating selection, although the simulated variance tends to be lower than has been measured in experimental studies. Our simulations also reveal that purging of deleterious mutations does not depend on the variance in their selection coefficient. Finally, an evolutionary analysis shows that, in contrast to previous theoretical approaches, intermediate selfing rates are never evolutionarily stable when the variation in inbreeding depression is due to fluctuations in the selection coefficient on deleterious mutations. 相似文献
164.
The rate of synonymous substitution in enterobacterial genes is inversely related to codon usage bias 总被引:31,自引:14,他引:31
Genes sequences from Escherichia coli, Salmonella typhimurium, and other
members of the Enterobacteriaceae show a negative correlation between the
degree of synonymous-codon usage bias and the rate of nucleotide
substitution at synonymous sites. In particular, very highly expressed
genes have very biased codon usage and accumulate synonymous substitutions
very slowly. In contrast, there is little correlation between the degree of
codon bias and the rate of protein evolution. It is concluded that both the
rate of synonymous substitution and the degree of codon usage bias largely
reflect the intensity of selection at the translational level. Because of
the high variability among genes in rates of synonymous substitution,
separate molecular clocks of synonymous substitution might be required for
different genes.
相似文献
165.
Evaluation of Virulence Test Procedures for Yersinia enterocolitica Recovered from Foods 总被引:9,自引:1,他引:8
W. H. LEE R. E. SMITH J. M. DAMARÉ M. E. HARRIS R. W. JOHNSTON 《Journal of applied microbiology》1981,50(3):529-539
Recently a heat stable toxin (ST) and the vw factors of the plague bacteria were identified in Yersinia enterocolitica recovered from human infections. The vw factors were reported to be associated with a plasmid of 42-46 M Daltons in size and were essential for the expression of virulence. With this knowledge virulence tests were developed which allowed us to assess the virulence potential of food-borne Y. enterocolitica regardless of biotypes or serotypes. The tests evaluated were: (1) rapid presumptive test for the virulence plasmid; (2) gel electrophoretic confirmation of the virulence plasmid; (3) Laird's qualitative oral feeding test with thirst stressed mice; (4) quantitative LD50 determination by i.p. injection of the mouse lethal ( i.e. serotype 0:8) strains in saline; (5) quantitative LD50 determination of mouse non-lethal ( i.e. serotype 0:3) strains by i.p. injection of these strains suspended in 1 ml of 10% iron dextran saline solution for virulence enhancement. These tests were evaluated with the serotypes 0:3 and 0:8 strains associated with human infections with and without the virulence plasmid with reproducible results. Then the virulence tests procedures were applied to 79 food isolates. The virulence plasmid was detected only in the Nilehn biotype 2, 3 and 4 strains, but it was absent in Nilehn biotype 1 or the atypical strains that ferment rhamnose. The virulence of food and clinical isolates of Y. enterocolitica can be assayed fairly accurately with the above tests. 相似文献
166.
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170.
Molecular evolution of bacteriophages: evidence of selection against the recognition sites of host restriction enzymes 总被引:12,自引:0,他引:12
Restriction enzymes produced by bacteria serve as a defense against
invading bacteriophages, and so phages without other protection would be
expected to undergo selection to eliminate recognition sites for these
enzymes from their genomes. The observed frequencies of all restriction
sites in the genomes of all completely sequenced DNA phages (T7, lambda,
phi X174, G4, M13, f1, fd, and IKe) have been compared to expected
frequencies derived from trinucleotide frequencies. Attention was focused
on 6-base palindromes since they comprise the typical recognition sites for
type II restriction enzymes. All of these coliphages, with the exception of
lambda and G4, exhibit significant avoidance of the particular sequences
that are enterobacterial restriction sites. As expected, the sequenced
fraction of the genome of phi 29, a Bacillus subtilis phage, lacks Bacillus
restriction sites. By contrast, the RNA phage MS2, several viruses that
infect eukaryotes (EBV, adenovirus, papilloma, and SV40), and three
mitochondrial genomes (human, mouse, and cow) were found not to lack
restriction sites. Because the particular palindromes avoided correspond
closely with the recognition sites for host enzymes and because other
viruses and small genomes do not show this avoidance, it is concluded that
the effect indeed results from natural selection.
相似文献