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81.
83.
Frequent derepression of G6PD and HPRT on the marsupial inactive X chromosome associated with cell proliferation in vitro 总被引:1,自引:0,他引:1
X chromosome dosage compensation in Marsupials is like that in eutherian mammals except that the paternal X chromosome is always inactive, and silence of this chromosome is not well maintained. We previously showed that the unstable inactivation of the paternal G6PD allele is associated with the lack of DNA methylation in the 5' CpG cluster. Even though this CpG island is unmethylated, the paternal allele (marked by an enzyme variant) is at least partially and often severely repressed in most tissues of the opossum, so that factors other than methylation must inactivate the locus. Here we report that when cell cultures are established from these tissues, the silent G6PD locus is depressed. Although often complete, the extent of derepression differs among tissues and within different cell types in the same tissue, and is not accompanied by obvious changes in the pattern of chromosome replication. Studies of the HPRT locus in these cells show that the paternal HPRT allele also derepresses in cultured cells. These observations suggest that without DNA methylation to maintain the silence of the locus, tissue or cell-specific factors act to repress the silent locus, but are unable to maintain inactivity through cell division, or are lost as cells proliferate in culture. 相似文献
84.
We have studied the 35Cl- NMR line broadening in the presence of photosystem II (PS II) membranes from spinach in the dark. In the presence of NH3 (which other work has shown to competitively inhibit chloride binding to PS II) we observed no decrease in 35 Cl- linewidths. We conclude that binding of Cl- to the O2 evolving center in PS II in the dark (previously demonstrated by EPR) is in slow exchange on the NMR timescale. We assign the observed line broadening to interaction with non-specific binding sites and with free paramagnetics. 相似文献
85.
Isolation and structure of corazonin, a cardioactive peptide from the American cockroach 总被引:11,自引:0,他引:11
Corazonin, a new cardioaccelerating peptide, has been isolated from the corpora cardiaca of the American cockroach, Periplaneta americana, and its structure determined to be Glp-Thr-Phe-Gln-Tyr-Ser-Arg-Gly-Trp-Thr-Asn-amide. The peptide stimulated heart beat at concentrations as low as 0.2 nM, which makes it the most potent insect cardioactive neuropeptide. 相似文献
86.
Jan Holgersson Michael E Breimer Anita Jacobsson Lola Svensson Ami Ulfvin Bo E Samuelsson 《Glycoconjugate journal》1990,7(6):601-608
Total non-acid glycolipid fractions and total sodium dodecylsulphate (SDS) solubilized protein fractions were isolated from human thrombocytes obtained from single human donors having different blood group A1/A2 phenotypes. The blood group A glycolipid antigens were characterized by immunostaining of thin layer plates with different monoclonal anti-A antibodies. The glycoproteins carrying blood group A epitopes were identified by SDS-PAGE and Western blot analysis using a monoclonal anti-A antibody. Blood group A glycolipid antigens were found in both A1 and A2 thrombocytes but the A2 individuals expressed at least ten times less A glycolipids compared to the A1 individuals. Expression of A type 3/4 chain and small amounts of A type 1 chain glycolipids were seen in thrombocytes of both A1 and A2 individuals, while the type 2 chain A glycolipids appeared to be missing from the A2 thrombocytes. Blood group A reactive glycoproteins were only found in thrombocytes of A1 individuals and could not be detected in A2 individuals or a blood group O individual. The major blood group A glycoprotein were found as a double band migrating in the 130 kDa region.Abbreviations SDS
sodium dodecyl sulfate
- PAGE
polyacrylamide gel electrophoresis
- HPTLC
high performance thin layer chromatography
- CBB
Coomassie brilliant blue
- GVH
graft versus host
Part of this work was presented at the Xth International Symposium on Glycoconjugates, Jerusalem, Israel. September, 1989.In the short hand designation for glycolipids, the letter indicate blood group determinant, the first numeral, the number of sugar residues, and the second numeral, the type of carbohydrate chain. Thus, A-6-1 means a hexaglycosylceramide with a blood group A determinant based on the type 1 carbohydrate chain. 相似文献
87.
Wolfgang Ludwig Michael Weizenegger Silvia Dorm Jan Andreesen Karl Heinz Schleifer 《FEMS microbiology letters》1990,71(1-2):139-143
A 1330 base-pair fragment of a 16S rRNA gene has been amplified, cloned and sequenced. Comparison to other 16S rRNA sequences of eubacteria showed that P. niger represents a deep branch within the subdivision "Gram-positive with Gram-negative cell walls". It is not related to peptostreptococci, representatives of this genus studied so far are more closely related to clostridia. 相似文献
88.
Jan T. Keltjens Ben W. te Brömmelstroet ServéW.M. Kengen Chris van der Drift Godfried D. Vogels 《FEMS microbiology letters》1990,87(3-4):327-332
Abstract In the process of methanogenesis, 5,6,7,8-tetrahydromethanopterin (H4 MPT) is the carrier of the C1 unit at the formyl through methyl state of reduction. By the transfer of a formyl group from formylmethanofuran, 5-formyl- and 10-formyl-H4 MPT are formed in hydrogenotrophic and methylotrophic organisms, respectively. Cyclohydrolysis of the 5- and 10-formyl derivatives then yields 5,10-methenyl-H4 MPT, which is reduced in two subsequent coenzyme F420 -dependent reactions to 5-methyl-H4 MPT. Following the transfer of the methyl group to coenzyme M, the substrate of the terminal step in methanogenesis, methylcoenzyme M, is produced. In this paper properties of the enzymes catalyzing the individual H4 MPT-dependent reactions are discussed. 相似文献
89.
90.