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11.
12.
Estimators of the Mantel-Haenszel variance consistent in both sparse data and large-strata limiting models 总被引:5,自引:0,他引:5
This paper proposes a new estimator of the variance of the Mantel-Haenszel estimator of common odds ratio that is easily computed and consistent in both sparse data and large-strata limiting models. Monte Carlo experiments compare its performance to that of previously proposed variance estimators. 相似文献
13.
We studied the frequencies and types of excision events which can occur with a retroviral shuttle vector containing the simian virus 40 origin of DNA replication. Analysis of the recloned vector plasmids by size and restriction enzyme mapping indicated that most contain one long terminal repeat. By hybridizing the plasmids to a mouse genomic repetitive DNA probe, we also determined that approximately 1 to 3% contain transduced cellular DNA sequences. 相似文献
14.
Bombyx mori 28S ribosomal genes contain insertion elements similar to the Type I and II elements of Drosophila melanogaster. 总被引:12,自引:0,他引:12
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We have examined the 28S ribosomal genes of the silkmoth, Bombyx mori, for the presence of insertion sequences. Two types of insertion sequences were found, each approximately 5 kb in length, which do not share sequence homology. Comparison of the nucleotide sequences of the junction regions with the uninserted gene reveals that one type of insertion has resulted in a 14 bp duplication of the 28S coding region at the insertion site. The location of this insertion and the 14 bp duplication are identical to that found in the Type I ribosomal insertion element of Drosophila melanogaster. The second type of insertion element is located at a site corresponding to approximately 75 bp upstream of the first type. The location of this insertion, the variability detected at its 5' junction, and a short region of sequence homology at its 3' junction suggest that it is related to the Type II element of D. melanogaster. This is the first example of a Type II-like rDNA insertion outside of sibling species of D. melanogaster, and the first example of a Type I-like rDNA insertion outside of the higher Diptera. 相似文献
15.
16.
The initial impact of computer assisted preventive screening in general practice consultations has been monitored. The technology has not been found stressful by patients, and the power of the consultation to alleviate low arousal has been increased by computer use. No appreciable increase in the durations of consultation was detected, despite an average computer initiated input of two minutes eight seconds. The computer has successfully prompted preventive screening and health education with a sixfold increase in the number of potentially relevant procedures being mentioned. The actual information presented by the computer has been shown to be crucial, with the terminal''s mere presence an ineffective reminder. The computer terminal was used in 65% of the consultations for which it was available, which, if sustained, represents an effective screening programme for attending patients. 相似文献
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18.
Summary Anthraquinones produced by suspension cultures of Cinchona ledgeriana are released into the medium, which becomes saturated with products late in the growth cycle. When a high affinity polymeric adsorbent, such as the macro-reticular Amberlite XAD-7, is added to the culture the concentration of anthraquinone in the medium is maintained at a low level and production may be stimulated 15-fold, yielding up to 20 mg/1/day. More than 90% of the product is released from the cells. For maximal yields it is shown that both the amount of adsorbent used and the time after sub-culture at which it is added to the system are critical. The value of such a method for product recovery from immobilised cells is discussed. 相似文献
19.
Synthesis of 5-chloroformycin A, 5-chloro-2''-deoxyformycin A and certain related 5,7-disubstituted 3-beta-D-ribofuranosylpyrazolo[4,3-d] pyrimidines from formycin A.
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K G Upadhya Y S Sanghvi R K Robins G R Revankar B G Ugarkar 《Nucleic acids research》1986,14(4):1747-1764
A facile synthesis of 7-amino-5-chloro-3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine (5-chloroformycin A, 6), 7-amino-5-chloro-3-(2-deoxy-beta-D-erythro-pentofuranosyl) pyrazolo [4,3-d]-pyrimidine (5-chloro-2'-deoxyformycin A, 13) and certain related 5,7-disubstituted pyrazolo[4,3-d]pyrimidine ribonucleosides is described starting with formycin A. Thiation of tri-O-acetyloxoformycin B (4b) with phosphorus pentasulfide, followed 3-beta-D-ribofuranosyl-7-thioxopyrazolo[4,3-d] pyrimidin-5(1H,4H,6H)-one (3b) in excellent yield. Chlorination of 4b with either phosphorus oxychloride or phenyl phosphonicdichloride furnished the key intermediate 5,7-dichloro-3-(2,3, 5-tri-O-acetyl-beta-D-ribofuranosyl)pyrazolo[4,3-d]pyrimidine (5a), which on deacetylation afforded 5,7-dichloro-3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine (5b). Ammonolysis of 5a with liquid ammonia gave 6, whereas with MeOH/NH3, a mixture of 6 and 7-methoxy-5-chloro-3-beta-D-ribofuranosylpyrazolo[4,3-d]pyrimidine (7) was obtained. Reaction of 6 with lithium azide and subsequent hydrogenation afforded 5-aminoformycin A (10). Treatment of 5a with thiourea gave 5-chloro-3-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl) pyrazolo[4,3-d]pyrimidine-7(1H,6H)-thione (8a), which on further reaction with sodium hydrosulfide furnished 3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine-5,7(1H,4H,6H)-dithione (11). The four-step deoxygenation procedure using phenoxythiocarbonylation of the 2'-hydroxy group of the 3', 5'-protected 6 gave 5-chloro-2'-deoxyformycin A (13). 相似文献
20.
In a variety of tumour systems, individuals carrying progressively growing neoplasms have lymphoid cells with a specific cytotoxic effect on cultured tumour cells from the same individual1–4. Since the sera of tumour-bearing individuals have been shown to prevent tumour cell destruction by immune lymphocytes in vitro2,5–8 and since this serum blocking activity appears early in primary and transplant tumour development5,7, it has been suggested that the appearance of this serum blocking activity might be responsible for the progressive growth of tumours in individuals having cytotoxic lymphocytes. Counteraction of this blocking activity would thus be of primary importance in facilitating the function of an already existing or bolstered cell-mediated immunity. The serum blocking activity might be inhibited in various ways, by preventing the formation of blocking antibody or by interfering with its action (“unblocking”), as demonstrated in Moloney sarcoma regressor sera9. This type of serum also has a therapeutic effect on Moloney sarcomas in vivo10,11, which has been tentatively attributed to its unblocking activity8,9 or, possibly, to a complement-dependent cytotoxicity10. Tumour growth in the Moloney sarcoma system, however, might be due in part to continuous recruitment of neoplastic cells by virus-induced transformation and so the therapeutic effect could be due to a virus-neutralizing serum activity9,10. 相似文献