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991.
Summary The recombination fraction between the interstitially located gene an and interchange 303 of rye was found to be 0.244±0.038 in a test cross using the translocation as the male parent. In first metaphase translocation configurations in pollen mother cells of the same plant, the chiasma frequency between an and the translocation breakpoint was found to be significantly more than twice the recombination fraction. Recombination was concluded to be masked by a difference in the alternate frequency between configurations without interstitial chiasmata and configurations with interstitial chiasmata, the effect of the first type being of major importance. Random centromere orientation of translocation multivalents with interstitial chiasmata was concluded to be a realistic assumption. The exceptionally high recombination between an and translocation 303 is discussed. Consideration is also given to the use of interchanges in the establishment of a marker's chromosomal position, and to the use of translocation chromosomes in balanced systems for hybrid breeding purposes.  相似文献   
992.
993.
A human diploid cell line of choroid origin was isolated from the retrouveal portion of an enucleated eye and designated HC. After 10 passages, when the proliferative capacity of HC cells decreased, they were infected and transformed by Simian Virus 40 (SV40). A proliferating long-term cultured cell line designated HC/SV40 was established and it has been maintained as monolayer for more than 100 passages so far. The two cell lines, HC and HC/SV40, were compared for growth characteristics, capacity to form colonies in soft agar, presence of nuclear T-antigen, and ultrastructure. Cytogenetic analysis was also performed to determine the presence of chromosomal aberrations due to the permanent viral transformation of the cell line. The results indicate that HC/SV40 should be considered the transformed counterparts of HC cells because they are morphologically similar to the latter but can grow in soft agar, possess T-antigen, and show a pattern of karyotypic changes similar to that induced by SV40 in human fibroblasts. The choroid origin of HC and HC/SV40 cell lines was confirmed by the presence, in their cytoplasm, of typical electron dense granules. Their neural origin will make these cell lines very useful for neuropharmacological and differentiation studies.  相似文献   
994.
995.
Depletion of intracellular potassium (K+) caused a marked reduction in the rate of endocytosis of receptor-bound low density lipoprotein (LDL) and epidermal growth factor (EGF) in human fibroblasts. K+ could be depleted slowly by a 3-hr incubation of cells in isotonic K+-free buffer. Rapid K+ depletion was induced by incubation of cells for 5 min with hypotonic medium, followed by transfer to isotonic K+-free buffer. Within 30 min of this treatment, cellular K+ levels fell by more than 60%. When the K+ level fell below a threshold of 40% of normal, the number of coated pits declined by 80% and the rate of endocytosis of 125I-LDL decreased by 70 to 95% despite normal to increased receptor binding. Similar results were obtained with 125I-epidermal growth factor. Addition of KCl to the culture medium up to 2 hr after K+ depletion restored cellular K+ levels and returned endocytosis of 125I-LDL promptly to normal. RbCl was as effective as KCl, but CsCl, LiCl, and (CH3)4NCl had no effect. Restoration by KCl was blocked by ouabain, indicating that uptake via the Na+/K+ ATPase was required. These data demonstrate that depletion of intracellular K+ reversibly arrests coated pit formation and receptor-mediated endocytosis in human fibroblasts.  相似文献   
996.
The replication and incompatibility region of the IncFVI plasmid pSU502 has been isolated by in vitro DNA manipulation as part of a 12.6 kb plasmid, denominated pSU503. Plasmid pSU503 was strongly incompatible with its parental plasmid, pSU1, but was fully compatible with the haemolytic plasmids pSU316 (IncFIII/IV), pHly152 (IncI2) and pSU233 (Inc-pSU233). Furthermore, the 6.9 kb EcoRI fragment of pSU503 which carries the replication and incompatibility determinants of pSU1 did not show any detectable homology (less than 70%) with any of the haemolysin-determining plasmids with which it is compatible. Thus, homologous haemolysin determinants have become linked to apparently unrelated replicons.  相似文献   
997.
A number of cytochemical parameters of the hemocytes of larval Galleria mellonella, an insect frequently used as a model by comparative cellular immunologists, are described. Cytochemical methods were used to quantify hemocyte granule-associated components, the results are compared to those obtained for leukocytes from higher animals. Granulocytes contained a population of nonlysosomal granules rich in mucopolysaccharide not seen in plasmatocytes. The numbers and dimensions of these granules showed a positive correlation to cell size, probably reflecting a developmental sequence in granulocyte maturation. Both granulocytes and plasmatocytes had other granules containing the typical lysosomal enzymes, acid phosphatase, beta-glucuronidase, esterase, and lysozyme. The nonlysosomal enzyme alkaline phosphatase was not found in Galleria hemocytes; it is also absent from vertebrate monocytes, macrophages, and immature polymorphonuclear leukocytes. Insect hemocytes appear to lack certain components of antibacterial systems typical of mammalian blood cells, such as H2O2-generating systems, cationic proteins, and myeloperoxidase. The bactericidal mechanisms of hemocytes probably involve lysozyme, as well as other biologically active cellular and humoral factors unique to insects.  相似文献   
998.
Ecdysteroids were analysed with radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC) in females of the apterygotous insect Thermobia domestica, which ahs overlapping moulting and reproductive cycles. During each moulting cycle, a peak in the haemolymph concentration of ecdysteroids occurs at day 9 (in the 11-day standard cycle), which can be correlated with apolysis and the beginning of new cuticle deposition. The ovaries show a peak of ecdysteroids at day 5 (i.e. one day before egg-laying), which suggests that these hormones are also involved in the reproductive cycle. In both cases, HPLC analysis combined with RIA suggests that the main ecdysteroid is 20-hydroxyecdysone. This duality in the function of ecdysteroids is discussed.  相似文献   
999.
Comparison of AMP and NADH binding to glycogen phosphorylase b   总被引:3,自引:0,他引:3  
The binding sites for the allosteric activator, AMP, to glycogen phosphorylase b are described in detail utilizing the more precise knowledge of the native structure obtained from crystallographic restrained least-squares refinement than has hitherto been available. Localized conformational changes are seen at the allosteric effector site that include shifts of between 1 and 2 A for residues Tyr75 and Arg309 and very small shifts for the region of residues 42 to 44 from the symmetry-related subunit. Kinetic studies demonstrate that NADH inhibits the AMP activation of glycogen phosphorylase b. Crystallographic binding studies at 3.5 A resolution show that NADH binds to the same sites on the enzyme as AMP, i.e. the allosteric effector site N, which is close to the subunit-subunit interface, and the nucleoside inhibitor site I, which is some 12 A from the catalytic site. The conformations of NADH at the two sites are different but both conformations are "folded" so that the nicotinamide ring is close (approx. 6 A) to the adenine ring. These conformations are compared with those suggested from solution studies and with the extended conformations observed in the single crystal structure of NAD+ and for NAD bound to dehydrogenases. Possible mechanisms for NADH inhibition of phosphorylase activation are discussed.  相似文献   
1000.
The "colicin" fragments comprising the 49 3'-terminal nucleotides of 16 S ribosomal RNA have been isolated from wild-type Escherichia coli and from a kasugamycin-resistant mutant that lacks methylation of two geminal adenine residues. Proton nuclear magnetic resonance (n.m.r.) spectra (500 MHz) were recorded at various temperatures. The low-field resonances arising from the hydrogen-bonded iminoprotons of paired bases were assigned using the nuclear Overhauser effect (n.o.e.). Crucial to the interpretation of the spectra are the resonances that originate from the two hydrogen-bonded iminoprotons of a U X G basepair. Combined with temperature-jump relaxation kinetics experiments the n.o.e.s lead to the conclusion that a conserved A X U/U X G junction in the hairpin is a thermolabile dislocation in the helix. The n.m.r. spectra of the wild-type and mutant fragment are only different with respect to the iminoproton resonances of the two base-pairs adjoining the hairpin loop. The spectra recorded at various temperatures tend to indicate that dimethylation of the adenosines labilizes these base-pairs, but no definitive conclusions are drawn. The results confirm our previous views that dimethylation of the adenosine residues affects the conformation of the hairpin loop.  相似文献   
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