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41.
Nonneutral evolution of tandem repeats in the mitochondrial DNA control region of lagomorphs 总被引:7,自引:0,他引:7
Casane D; Dennebouy N; de Rochambeau H; Mounolou JC; Monnerot M 《Molecular biology and evolution》1997,14(8):779-789
The mitochondrial DNA of the European rabbit (Oryctolagus cuniculus)
contains a tandem array of 153-bp repeats in the vicinity of the
replication origin of the H-stand. Variation among molecules in the number
of these repeats results in inter- and intraindividual length polymorphism
(heteroplasmy). Generally, in an individual, one predominant molecular type
is observed, the others representing a low percentage of the mtDNA content.
At the tissue level, we observe a particular distribution of this
polymorphism in the gonads compared with liver, kidneys, or brain, implying
a relationship between the differentiation status of the cells and the
types of new mtDNA molecules which appear and accumulate during lifetime.
Similar tandem repeats were also found in the mtDNA noncoding region of
European hares (Lepus europaeus), a cottontail (Sylvilagus floridanus), and
a pika (Ochotona rufescens). The lengths and the sequences of these units
evolve rapidly and in a concerted way, but the number of repeats is
maintained in a narrow range, and an internal 20-bp segment is highly
conserved. Constraints restrict the evolution of the primary sequence of
these repeated units, the number of which is probably controlled by a
stabilizing selection.
相似文献
42.
The 0 degree C closed complexes between Escherichia coli RNA polymerase and two promoters, T7-A3 and lacUV5 总被引:5,自引:0,他引:5
R T Kovacic 《The Journal of biological chemistry》1987,262(28):13654-13661
The promoter-specific binding of Escherichia coli RNA polymerase to the T7-A3 and the lacUV5 promoters at 0 degrees C was analyzed by DNase I footprinting. At 37 degrees C, the footprint from RNA polymerase bound to the A3 promoter is essentially the same as that reported by Galas, D.J., and Schmitz, A., (1978) Nucleic Acids Res. 5, 3157-3170 for the lacUV5 promoter. At 0 degrees C, the footprint for the A3 promoter is well defined but reduced in size. The principal difference between the 0 and 37 degrees C footprints is a region from -2 to +18 which is protected by polymerase at the higher but not at the lower temperature. In contrast, the 0 degree C footprint for the lacUV5 promoter differs substantially in character from the footprint for A3 at 0 degree C. The footprint is similar to the pattern of DNase I digestion of DNA bound to a surface; alternating regions of sensitive and protected DNA are spaced at intervals of about 10 base pairs. This region of DNase I-sensitive and -resistant DNA has the same boundaries as the 0 degree C footprint on T7-A3. Temperature shift experiments confirmed the sequence specificity of the RNA polymerase interaction with UV5 at 0 degree C. These results indicate that RNA polymerase binds specifically to each promoter sequence in a closed complex. The increased time and amounts of RNA polymerase required to form the 0 degree C footprint on the lacUV5 promoter indicate that it binds RNA polymerase more weakly than does the T7-A3 promoter. Therefore there is a correlation between the binding constant for closed complex formation estimated from kinetic measurements and the formation of the 0 degree C footprint. The -35 region of the promoter may be more important in establishing the 0 degree C footprint because the T7-A3 promoter is a better match to the consensus sequence. Conversely, the -10 region seems less important because lacUV5 is a perfect match to the consensus, whereas the T7-A3 promoter matches at only five out of seven positions. The 0 degree C footprints encompass both regions along with the spacer; the combination of these regions rather than an individual region may determine the character of the footprint and the magnitude of the binding constant. 相似文献
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Molecular evolution of mitochondrial 12S RNA and cytochrome b sequences in the pantherine lineage of Felidae 总被引:4,自引:2,他引:2
DNA sequence comparisons of two mitochondrial DNA genes were used to infer
phylogenetic relationships among 17 Felidae species, notably 15 in the
previously described pantherine lineage. The polymerase chain reaction
(PCR) was used to generate sequences of 358 base pairs of the mitochondrial
12S RNA gene and 289 base pairs of the cytochrome b protein coding gene.
DNA sequences were compared within and between 17 felid and five nonfelid
carnivore species. Evolutionary trees were constructed using phenetic,
cladistic, and maximum likelihood algorithms. The combined results
suggested several phylogenetic relationships including (1) the recognition
of a recently evolved monophyletic genus Panthera consisting of Panthera
leo, P. pardus, P. onca, P. uncia, P. tigris, and Neofelis nebulosa; (2)
the recent common ancestry of Acinonyx jubatus, the African cheetah, and
Puma concolor, the American puma; and (3) two golden cat species, Profelis
temmincki and Profelis aurata, are not sister species, and the latter is
strongly associated with Caracal caracal. These data add to the growing
database of vertebrate mtDNA sequences and, given the relatively recent
divergence among the felids represented here (1-10 Myr), allow 12S and
cytochrome b sequence evolution to be addressed over a time scale different
from those addressed in most work on vertebrate mtDNA.
相似文献
46.
Sea urchin Hox genes: insights into the ancestral Hox cluster 总被引:3,自引:0,他引:3
We describe the Hox cluster in the radially symmetric sea urchin and
compare our findings to what is known from clusters in bilaterally
symmetric animals. Several Hox genes from the direct-developing sea urchin
Heliocidaris erythrogramma are described. CHEF gel analysis shows that the
Hox genes are clustered on a < or = 300 kilobase (kb) fragment of DNA,
and only a single cluster is present, as in lower chordates and other
nonvertebrate metazoans. Phylogenetic analyses of sea urchin, amphioxus,
Drosophila, and selected vertebrate Hox genes confirm that the H.
erythrogramma genes, and others previously cloned from other sea urchins,
belong to anterior, central, and posterior groups. Despite their radial
body plan and lack of cephalization, echinoderms retain at least one of the
anterior group Hox genes, an orthologue of Hox3. The structure of the
echinoderm Hox cluster suggests that the ancestral deuterostome had a Hox
cluster more similar to the current chordate cluster than was expected Sea
urchins have at least three Abd-B type genes, suggesting that Abd-B
expansion began before the radiation of deuterostomes.
相似文献
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J R Ames U Hollstein A R Gagneux M D Ryan P Kovacic 《Free radical biology & medicine》1987,3(2):85-96
Cyclic voltammetry data were obtained for most of the main categories of antiamebic agents, specifically, quinones, heterocyclic nitro compounds, metal derivatives and chelators, and iminium-type ions. The reductions (our data and literature values) were for the most part reversible, with potentials usually in the favorable range of +0.10 to -0.56 V. The drug effect is believed to result generally from the catalytic production of oxidative stress usually arising from the formation of superoxide via electron transfer. In addition, relevant literature data are provided. 相似文献