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41.
αAIns, an elongated α-crystallin A chain previously observed in rat, was present beside the normal αA chain in mouse, gerbil and hamster, which places its origin at least 30 million years ago. Like in rat the sequences of golden hamster αAIns and αA were found to be identical, apart from the internal insertion of 22 residues in αAIns. The hamster chains only differed from the rat chains by a single substitution in the inserted sequence of αAIns. The origin of αAIns, by insertion of 22 residues in an otherwise unchanged αA chain, and its rigid evolutionary conservation are most easily explained by assuming the incomplete removal of a putative intervening sequence from the precursor mRNA of αA, leaving an intracistronic insert of 66 nucleotides in part of the eventually translated mRNA.  相似文献   
42.
Summary Previous use of hemolysis time measurement to determine permeability coefficients for the red blood cell membrane rested on the assumption that cells swelling in a hypotonic medium hemolyzed immediately on reaching critical volume. By preswelling red cells to various volumes prior to immersion in hemolytic solutions we extrapolate to the hemolysis time of red cells immersed at critical volume and thereby find a significant period of time during which the cells apparently remain in a spherical form prior to release of hemoglobin. Revised estimates of permeability coefficients follow from including this spherical (nonswelling) phase. In addition, the appreciation of a characteristic time period during which the membrane is under tension provides new opportunity to study physical and chemical properties of the membrane.Presented in part at the 1974 joint meeting of the Biophysical Society and the American Society of Biological Chemists.  相似文献   
43.
SpecificityH-2.7 is expressed predominantly on erythrocytes and controlled by a gene that maps within theH-2 gene complex at a locus, designated asH-2G, which apparently lies between regionsS andD. Three phenotypes have been observed with respect to this antigen: a) positive by direct test and absorption (haplotypesH-2 f ,H-2 j ,H-2 p ,H-2 s ); b) positive only by absorption (H-2 k ); and c) negative (H-2 b ,H-2 d ,H-2 q ). New crossover positions have been established for severalH-2 recombinants based on classifications for theH-2G locus.  相似文献   
44.
Summary The endocrine pancreas of the bullhead catfish, Ictalurus nebulosus, and the channel catfish, I. punctatas was studied by light and electron microscopy. In addition to the usual A, B and D cells, a fourth endocrine cell type was consistently observed in the electron microscope. All endocrine cell types were innervated. The vesicles of most of the nerve endings were ultrastructurally different from typical adrenergic and cholinergic vesicles, strongly suggesting the possibility of a third autonomic neurotransmitter serving as a regulator of catfish islet secretion.Supported in part by PHS grant AM 11407 awarded to Dr. Bryce Munger.  相似文献   
45.
Earlier investigations disclose that some plant ribosome-inactivating proteins (RIPs) adversely affect mouse embryonic development. In the present study, a mushroom RIP, namely lyophyllin from Lyophyllum shimeji, was isolated, partially sequenced, and its translation inhibitory activity determined. Its teratogenicity was studied by using a technique entailing microinjection and postimplantation whole-embryo culture. It was found that embryonic abnormalities during the period of organogenesis from E8.5 to E9.5 were induced by lyophyllin at a concentration as low as 50 μg/ml, and when the lyophyllin concentration was raised, the number of abnormal embryos increased, the final somite number decreased, and the abnormalities increased in severity. The affected embryonic structures included the cranial neural tube, forelimb buds, branchial arches, and body axis, while optic and otic placodes were more resistant. Lyophyllin at a concentration higher than 500 μg/ml also induced forebrain blisters within the cranial mesenchyme. When the abnormal embryos were examined histologically, an increase of cell death was found to be associated with abnormal structures, indicating that cell death may be one of the underlying causes of teratogenicity of the mushroom RIP. This constitutes the first report on the teratogenicity of a mushroom RIP.  相似文献   
46.
47.
Ethanol can be produced from lignocellulosic biomass using steam pretreatment followed by enzymatic hydrolysis and fermentation. The sugar yields, from both hemicellulose and cellulose are critical parameters for an economically-feasible ethanol production process. This study shows that a near-theoretical glucose yield (96-104%) from acid-catalysed steam pretreated corn stover can be obtained if xylanases are used to supplement cellulases during hydrolysis. Xylanases hydrolyse residual hemicellulose, thereby improving the access of enzymes to cellulose. Under these conditions, xylose yields reached 70-74%. When pre-treatment severity was reduced by using autocatalysis instead of acid-catalysed steam pretreatment, xylose yields were increased to 80-86%. Partial delignification of pretreated material was also evaluated as a way to increase the overall sugar yield. The overall glucose yield increased slightly due to delignification but the overall xylose yield decreased due to hemicellulose loss in the delignification step. The data also demonstrate that steam pretreatment is a robust process: corn stover from Europe and North America showed only minor differences in behaviour.  相似文献   
48.
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) and the associated proteins (Cas) comprise a system of adaptive immunity against viruses and plasmids in prokaryotes. Cas1 is a CRISPR-associated protein that is common to all CRISPR-containing prokaryotes but its function remains obscure. Here we show that the purified Cas1 protein of Escherichia coli (YgbT) exhibits nuclease activity against single-stranded and branched DNAs including Holliday junctions, replication forks and 5'-flaps. The crystal structure of YgbT and site-directed mutagenesis have revealed the potential active site. Genome-wide screens show that YgbT physically and genetically interacts with key components of DNA repair systems, including recB, recC and ruvB. Consistent with these findings, the ygbT deletion strain showed increased sensitivity to DNA damage and impaired chromosomal segregation. Similar phenotypes were observed in strains with deletion of CRISPR clusters, suggesting that the function of YgbT in repair involves interaction with the CRISPRs. These results show that YgbT belongs to a novel, structurally distinct family of nucleases acting on branched DNAs and suggest that, in addition to antiviral immunity, at least some components of the CRISPR-Cas system have a function in DNA repair.  相似文献   
49.
Although Blm and Top3α are known to form a minimal dissolvasome that can uniquely undo a double Holliday junction structure, the details of the mechanism remain unknown. It was originally suggested that Blm acts first to create a hemicatenane structure from branch migration of the junctions, followed by Top3α performing strand passage to decatenate the interlocking single strands. Recent evidence suggests that Top3α may also be important for assisting in the migration of the junctions. Using a mismatch-dHJ substrate (MM-DHJS) and eukaryotic Top1 (in place of Top3α), we show that the presence of a topoisomerase is required for Blm to substantially migrate a topologically constrained Holliday junction. When investigated by electron microscopy, these migrated structures did not resemble a hemicatenane. However, when Blm is together with Top3α, the dissolution reaction is processive with no pausing at a partially migrated structure. Potential mechanisms are discussed.  相似文献   
50.
Prediction accuracies of estimated breeding values for economically important traits are expected to benefit from genomic information. Single nucleotide polymorphism (SNP) panels used in genomic prediction are increasing in density, but the Markov Chain Monte Carlo (MCMC) estimation of SNP effects can be quite time consuming or slow to converge when a large number of SNPs are fitted simultaneously in a linear mixed model. Here we present an EM algorithm (termed “fastBayesA”) without MCMC. This fastBayesA approach treats the variances of SNP effects as missing data and uses a joint posterior mode of effects compared to the commonly used BayesA which bases predictions on posterior means of effects. In each EM iteration, SNP effects are predicted as a linear combination of best linear unbiased predictions of breeding values from a mixed linear animal model that incorporates a weighted marker-based realized relationship matrix. Method fastBayesA converges after a few iterations to a joint posterior mode of SNP effects under the BayesA model. When applied to simulated quantitative traits with a range of genetic architectures, fastBayesA is shown to predict GEBV as accurately as BayesA but with less computing effort per SNP than BayesA. Method fastBayesA can be used as a computationally efficient substitute for BayesA, especially when an increasing number of markers bring unreasonable computational burden or slow convergence to MCMC approaches.  相似文献   
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