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排序方式: 共有143条查询结果,搜索用时 390 毫秒
61.
62.
John W. Taylor Beverly D. Smolich Georgiana May 《Evolution; international journal of organic evolution》1986,40(4):716-739
We studied mitochondrial DNA variability in 19 natural Neurospora crassa isolates and one wild-type isolate to examine evolution of these fungi and their mitochondrial DNA (mtDNA). We combined restriction endonuclease analysis of natural isolate mtDNA with DNA-DNA hybridization to cloned EcoR I fragments of a wild-type genome to discriminate between length mutations and site changes due to nucleotide substitution. Most variability was due to length mutations (insertions and deletions); genome size could vary 25% between pairs of isolates. Length-mutation distribution was not random, nor simply explained by the presence of coding versus noncoding regions. Restriction-site changes were few; the estimated amount of nucleotide substitution per nucleotide between the most divergent pair of isolates was 0.78%. Evolutionary relationships among isolates based on both types of mutations were compatible, and suggest that geographically distinct populations of mitochondrial DNA exist in the biological species, N. crassa. In contrast, no such correlation was shown by the previously determined distribution of nuclear heterokaryon incompatibility genes in the same isolates (Mylyk, 1975, 1976). 相似文献
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B D Smolich S K Tarkington M S Saha R M Grainger 《Molecular and cellular biology》1994,14(2):1355-1363
Crystallins, the major gene products of the lens, accumulate to high levels during the differentiation of the vertebrate lens. Although crystallins were traditionally thought to be lens specific, it has recently been shown that some are also expressed at very low levels in nonlens tissues. We have examined the embryonic expression pattern of gamma-crystallins, the most abundant crystallins of the embryonic lens in Xenopus laevis. The expression profile of five Xenopus gamma-crystallin genes mirrors the pattern of lens differentiation in X. laevis, exhibiting on average a 100-fold increase between tailbud and tadpole stages. Four of these genes are also ubiquitously expressed outside the lens at a very low level, the first demonstration of nonlens expression of any gamma-crystallin gene; expression of the remaining gene was not detected outside the head region, thus suggesting that there may be two classes of gamma-crystallin genes in X. laevis. Predictions regarding control mechanisms responsible for this dual mode of expression are discussed. This study raises the question of whether any crystallin, on stringent examination, will be found exclusively in the lens. 相似文献
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67.
Glycosylation sites and site-specific glycosylation in human Tamm- Horsfall glycoprotein 总被引:4,自引:1,他引:3
The N-glycosylation sites of human Tamm-Horsfall glycoprotein from one
healthy male donor have been characterized, based on an approach using
endoproteinase Glu-C (V-8 protease, Staphylococcus aureus ) digestion and a
combination of chromatographic techniques, automated Edman sequencing, and
fast atom bombardment mass spectrometry. Seven out of the eight potential
N-glycosylation sites, namely, Asn52, Asn56, Asn208, Asn251, Asn298,
Asn372, and Asn489, turned out to be glycosylated, and the potential
glycosylation site at Asn14, being close to the N-terminus, is not used.
The carbohydrate microheterogeneity on three of the glycosylation sites was
studied in more detail by high-pH anion-exchange chromatographic profiling
and 500 MHz1H-NMR spectroscopy. Glycosylation site Asn489 contains mainly
di- and tri-charged oligosaccharides which comprise, among others, the
GalNAc4 S (beta1-4)GlcNAc terminal sequence. Only glycosylation site Asn251
bears oligomannose-type carbohydrate chains ranging from Man5GlcNAc2to
Man8GlcNAc2, in addition to a small amount of complex- type structures.
Profiling of the carbohydrate moieties of Asn208 indicates a large
heterogeneity, similar to that established for native human Tamm-Horsfall
glycoprotein, namely, multiply charged complex-type carbohydrate
structures, terminated by sulfate groups, sialic acid residues, and/or the
Sda-determinant.
相似文献
68.
Leo AB Joosten Erik Lubberts Monique MA Helsen Tore Saxne Christina JJ Coenen-de Roo Dick Heinegård Wim B van den Berg 《Arthritis research & therapy》1999,1(1):81-11
Destruction of cartilage and bone are hallmarks of human rheumatoid arthritis (RA), and controlling these erosive processes
is the most challenging objective in the treatment of RA. Systemic interleukin-4 treatment of established murine collagen-induced
arthritis suppressed disease activity and protected against cartilage and bone destruction. Reduced cartilage pathology was
confirmed by both decreased serum cartilage oligomeric matrix protein (COMP) and histological examination. In addition, radiological
analysis revealed that bone destruction was also partially prevented. Improved suppression of joint swelling was achieved
when interleukin-4 treatment was combined with low-dose prednisolone treatment. Interestingly, synergistic reduction of both
serum COMP and inflammatory parameters was noted when low-dose interleukin-4 was combined with prednisolone. Systemic treatment
with interleukin-4 appeared to be a protective therapy for cartilage and bone in arthritis, and in combination with prednisolone
at low dosages may offer an alternative therapy in RA. 相似文献
69.
The development of the atrioventricular bundle (AVB) and ventricular Purkinje system and their innervation have been studied in fetal sheep from 27 to 140 days gestation (term is 147 days). The AVB initially consisted of a primordium, which lacked innervation and was composed of small, relatively undifferentiated myocytes. Differentiation of Purkinje-like cells within the AVB began near its distal end and extended towards the atrioventricular node (AVN). Differentiation of the ventricular Purkinje system extended distally from the region of bifurcation of the AVB from cells that were indistinguishable from the working myocardium and continuous with the AVB primordium. Differentiation of Purkinje-like AVB cells was complete by 46 days gestation but Purkinje fibres were still differentiating within the ventricular wall at 60 days gestation. The main morphological changes included a large increase in cell size and organization into strands, development of characteristic glycogen-filled regions containing many intermediate filaments and early development of myofibrillar M lines compared to the working myocardium. The differentiation of AVB cells and the ventricular Purkinje system preceded their innervation. The AVB became innervated earlier than ventricular Purkinje fibres, intimate contacts between proximal AVB cells and nerve axons being present at 60 days gestation. Nerve fibres were present in the septomarginal band at this time, however, en passant associations with ventricular Purkinje fibres were rarely observed until 140 days gestation and intimate contacts were not present at any stage. Although the AVB and ventricular Purkinje system of adult sheep are composed of morphologically similar cells, the present study demonstrates that they differ in origin and their mode of differentiation as well as timing and intimacy of innervation. Innervation is not part of the developmental mechanism leading to the differentiation of Purkinje fibres. No primordium of the ventricular Purkinje system could be identified, suggesting that the mechanism of differentiation of ventricular Purkinje fibres involves recruitment from early working myocardium. 相似文献
70.