The region of the clock gene period (per) that encodes a repetitive tract
of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran
species both within and outside the Drosophilidae. All the non-
Drosophilidae sequences in this region are short and present a remarkably
stable picture compared to the Drosophilidae, in which the region is much
larger and extremely variable, both in size and composition. The
accelerated evolution in the repetitive region of the Drosophilidae appears
to be mainly due to an expansion of two ancestral repeats, one encoding a
Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and
asparagine or threonine. In some drosophilids the expansion involves a
duplication of the pentapeptide sequence, but in Drosophila pseudoobscura
both the dipeptide and the pentapeptide repeats are present in larger
numbers. In the nondrosophilids, however, the pentapeptide sequence is
represented by one copy and the dipeptide by two copies. These observations
fulfill some of the predictions of recent theoretical models that have
simulated the evolution of repetitive sequences.
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We have analyzed the conserved regions of the gene coding for the
circumsporozoite protein (CSP) in 12 species of Plasmodium, the malaria
parasite. The closest evolutionary relative of P. falciparum, the agent of
malignant human malaria, is P. reichenowi, a chimpanzee parasite. This is
consistent with the hypothesis that P. falciparum is an ancient human
parasite, associated with humans since the divergence of the hominids from
their closest hominoid relatives. Three other human Plasmodium species are
each genetically indistinguishable from species parasitic to nonhuman
primates; that is, for the DNA sequences included in our analysis, the
differences between species are not greater than the differences between
strains of the human species. The human P. malariae is indistinguishable
from P. brasilianum, and P. vivax is indistinguishable from P. simium; P.
brasilianum and P. simium are parasitic to New World monkeys. The human P.
vivax-like is indistinguishable from P. simiovale, a parasite of Old World
macaques. We conjecture that P. malariae, P. vivax, and P. vivax-like are
evolutionarily recent human parasites, the first two at least acquired only
within the last several thousand years, and perhaps within the last few
hundred years, after the expansion of human populations in South America
following the European colonizations. We estimate the rate of evolution of
the conserved regions of the CSP gene as 2.46 x 10(-9) per site per year.
The divergence between the P. falciparum and P. reichenowi lineages is
accordingly dated 8.9 Myr ago. The divergence between the three lineages
leading to the human parasites is very ancient, about 100 Myr old between
P. malariae and P. vivax (and P. vivax-like) and about 165 Myr old between
P. falciparum and the other two.
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Photosynthetic enhancement studies performed at 619 nm (excitation of Systems I and II) and at 446 nm (mainly excitation of System I) revealed an 18% photosynthetic enhancement simultaneously with a 31% reduction in glycolate excretion. This observation supports the hypothesis that some glycolate may be consumed in an oxidation process associated with System I when System II is poorly excited and the supply of electrons from the water splitting process of photosynthesis is low. 相似文献
Several 7-(hydroxy, amino, methylureido, and guanidino)alkynyl-substituted 8-aza-7-deaza- hypoxanthine analogues were investigated as potential universal nucleobases. 7-Aminobutynyl-8-aza-7-deazahypoxanthine was found to be the most promising quasi-universal nucleobase with improved hybridization and polymerase chain reaction (PCR) enhancing properties as compared to commonly used hypoxanthine (the nucleobase of inosine). It demonstrated improved ambiguity for pairing with A, T, and C bases and its base pairing properties can be summarized as follows: X:C~X:A~X:T > X:G. The improvement in PCR performance directly correlated with primer's Tm. Primers containing multiple 7-aminobutynyl-8-aza-7-deazahypoxanthines were successfully used without noticeable inhibition of Taq polymerase activity provided the modifications are positioned more than two bases away from the 3′ end. 相似文献
One can determine the best dilution of a primary antibody for immunohistochemistry that uses horseradish peroxidase conjugated to a secondary antibody by testing increasing concentrations sequentially on the same tissue section. When the same tissue section is incubated repeatedly with increasing concentrations of primary antibodies to epithelial membrane antigen, smooth muscle α-actin, or vimentin using alkaline phosphatase conjugated to a secondary antibody as the reporter, the best staining was obtained with a less concentrated primary antibody than was optimal for a single staining test. The best concentration of primary antibody for single run staining using an alkaline phosphatase reporting system is usually four times the best concentration for staining with multiple runs. The optimal concentration can be determined by denaturing the residual alkaline phosphatase and extracting residual stain by incubating the section in 4:1 diglyme:phosphate buffered saline for 20 min at 80o C between tests of primary antibody concentrations. I tested the method for four chromogens from one supplier and one chromogen from a different supplier. 相似文献
Treatments with high-voltage electrical discharges (HVED) and high-pressure homogenization (HPH) were studied and compared for the release of ionic components, carbohydrates, proteins, and pigments from microalgae Parachlorella kessleri (P. kessleri). Suspensions (1% w/w) of microalgae were treated by HVED (40 kV/cm, 1–8 ms) or by HPH (400–1200 bar, 1–10 passes). Particle-size distribution (PSD) and microscopic analyses were used to detect the disruption and damage of cells. HVED were very effective for the extraction of ionic cell components and carbohydrates (421 mg/L after 8 ms of the treatment). However, HVED were ineffective for pigments and protein extraction. The concentration of proteins extracted by HVED was just 750 mg/L and did not exceed 15% of the total quantity of proteins. HPH permitted an effective release overall of intracellular compounds from P. kessleri microalgae including a large quantity of proteins, whose release (at 1200 bar) was 4.9 times higher than that obtained by HVED. Consequently, HVED can be used at the first step of the overall extraction process for the selective recovery of low-molecular-weight components. HPH can be then used at the second step for the recovery of remaining cell compounds.
Bioprocess and Biosystems Engineering - Microalgae of Nannochloropsis sp. present valuable source of bio-molecules (pigments, lipids, proteins) that have nutritional potential for the... 相似文献
An antiparallel actin dimer has been proposed to be an intermediate species during actin filament nucleation. We now show that latrunculin A, a marine natural product that inhibits actin polymerization, arrests polylysine-induced nucleation at the level of an antiparallel dimer, resulting in its accumulation. These dimers, when composed of pyrene-labeled actin subunits, give rise to a fluorescent excimer, permitting detection during polymerization in vitro. We report the crystallographic structure of the polylysine-actin-latrunculin A complex at 3.5-A resolution. The non-crystallographic contact is consistent with a dimeric structure and confirms the antiparallel orientation of its subunits. The crystallographic contacts reveal that the mobile DNase I binding loop of one subunit of a symmetry-related antiparallel actin dimer is partially stabilized in the interface between the two subunits of a second antiparallel dimer. These results provide a potential explanation for the paradoxical nucleation of actin filaments that have exclusively parallel subunits by a dimer containing antiparallel subunits. 相似文献
In many electroporation applications mass transport in biological tissue is of primary concern. This paper presents a theoretical advancement in the field and gives some examples of model use in electroporation applications. The study focuses on post-treatment solute diffusion. 相似文献