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21.
Abstract: Gangliosides were previously reported to induce neuritogenesis in primary neuronal cultures and in some neurally derived cell lines. Because isolated gangliosides usually contain variable quantities of peptides, we investigated the possibility the neurite-stimulating activity could be caused by these contaminants. Ganglioside preparations from bovine brain and other sources were subjected to a three-step purification procedure that eliminated at least 95% of the contaminating peptides. These purfied preparations retained their capacity to induce extensive neurite growth in neuro-2A murine neuroblastoma. Proteolytic digestion and a number of additional procedures were used to reduce residual contamination further without loss of activity. Several crude ganglioside samples had negative effects on neurite development until freed of theri inhibitory factors, which were derived from the tissue and/or introduced during laboratory operations. This was particularly evident for bovine white matter gangliosides whose activity increased in proportion to peptide removal. When carefully purified, virtually all of 11 different gangliosides tested were highly active, with the possible exception of GM4, which demonstrated only moderate activity in a limited number of tests. All of the neutral glycolipids tested, as well as sulfatides and free sialic acid, were inactive.  相似文献   
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Glycogen-deficient yeast mutants grew more slowly than wild-type cells on certain nonfermentable carbon substrates. Revertant colonies could be detected on these lines.  相似文献   
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M E Byrne  D A Rouch  R A Skurray 《Gene》1989,81(2):361-367
Resistance to the aminoglycosides gentamicin, tobramycin and kanamycin (GmTmKmR) in Australian clinical strains of Staphylococcus aureus is commonly carried on the composite transposon Tn4001. The resistance gene aacA-aphD of Tn4001, which encodes a bifunctional AAC(6')-APH(2") modifying enzyme, is flanked by two 1324-bp inverted repeats, IS256L and IS256R, that are identical in sequence. Analysis of the IS256 sequence revealed structural features characteristic of IS elements including 26-bp imperfect terminal inverted repeats and a single open reading frame with coding capacity for a 45.6 kDa protein. The nucleotide sequence of IS256 described here, together with the sequence of the aacA-aphD gene reported previously [Rouch et al., J. Gen. Microbiol. 133 (1987) 3039-3052], completes the entire sequence of Tn4001, which totals 4566 bp.  相似文献   
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The relative importance of different sites of alkylation on DNA was determined by comparing two ethylating agents. 1-Ethyl-1-nitrosourea (ENU) ethylates DNA with a higher proportion of total adducts on ring oxygens than ethyl methanesulfonate, which ethylates with a higher proportion of total adducts on the N-7 of guanine. Research with somatic cells in culture and prokaryotes strongly suggests that O6-guanine (O6-G) is the principal genotoxic site. To determine the importance in germ-line mutagenesis of the O6-G site relative to the N-7 of guanine, dose-response curves were constructed for both ENU and EMS, where dose was measured as total adducts per deoxynucleotide (APdN) and response as sex-linked recessive lethals (SLRL) induced in Drosophila melanogaster spermatozoa. For both mutagens the dose response curve was linear and extrapolated to the origin. The dose-response curve for ENU was fit to an equation m = 6.2D, and the dose response curve for EMS, from this and previous experiments, was m = 3.2D where m = %SLRL and D = APdN X 10(-3). Therefore, ENU is 1.9 times more efficient per adduct in inducing SLRL mutations than EMS. In vitro studies showed that ENU induced 9.5% of its total adducts on O6-G while EMS induced 2.0% of its adducts on O6-G. If O6-G was the sole genotoxic site, then ENU should be 4.8 times more efficient per adduct than EMS. In contrast, if N-7 G was the sole genotoxic site, ENU would be only 0.19 as effective as EMS. It was concluded that while O6-G was the principal genotoxic site, N-7 G made a significant contribution to germ-line mutagenesis.  相似文献   
28.
Northern blot analysis revealed that a single 4.2 kb phytochrome mRNA species was detectable in cotyledons excised from five-day-old etiolated cucumber seedlings. Intact etiolated five-day-old cucumber seedlings were given a red light or benzyladenine treatment, and cotyledons were harvested at various times following treatment. The abundance of phytochrome mRNA in the cotyledons was quantitated using 32P-labeled RNA probes and slot blot analysis. By 2 h after irradiation the phytochrome mRNA level was reduced to 40% of the initial abundance and reaccumulation began by 3 h after irradiation. Reaccumulation of phytochrome mRNA to the time-zero dark control level was achieved by 10 h after treatment. A decrease in phytochrome mRNA abundance was evident by 2 h after benzyladenine treatment, and a maximal reduction to 45% of the time-zero dark control was attained by 4 h after treatment. No recovery of the phytochrome mRNA level was evident by 8 h after benzyladenine treatment. The abundance of actin mRNA was unaffected by benzyladenine treatment.  相似文献   
29.
Guide RNA-directed uridine insertion RNA editing in vitro.   总被引:12,自引:0,他引:12       下载免费PDF全文
E M Byrne  G J Connell    L Simpson 《The EMBO journal》1996,15(23):6758-6765
Guide RNAs (gRNAs) have been proposed to mediate uridine (U) addition/deletion editing of mitochondrial mRNAs in kinetoplastid protozoa. The Us are proposed to be derived either from UTP by two successive cleavage-ligations or transesterifications, or from the 3' end of the gRNA by the same mechanisms. We have demonstrated gRNA-dependent U insertions into a specific editing site of a pre-edited mRNA which was incubated in a mitochondrial extract from Leishmania tarentolae. The predominant number of U insertions was determined by the number of guiding nucleotides in the added gRNA, and the formation of a gRNA-mRNA anchor duplex was necessary for activity. UTP and alpha-beta bond hydrolysis of ATP were required, and the activity was inhibited above 50-100 mM KCl. A gRNA-independent insertion of up to approximately 13 Us occurred in the absence of the added cognate gRNA; the extent of this activity was affected by sequences upstream and downstream of the edited region. Heparin inhibited the gRNA-independent U insertion activity and had no effect on the gRNA-dependent activity. Blocking the 3' OH of the gRNA had little effect on the gRNA-dependent U insertion activity. The data are consistent with a cleavage-ligation model in which the Us are derived directly from UTP.  相似文献   
30.
We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.   相似文献   
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