Biomedical subjects
Publications and source records attributed to Q Li.
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The genus Murraya has been widely used in traditional medicine in east Asia. In view of the recent isolation of the anti-implantation alkaloid yuehchukene from M. paniculata a search has now been made for other natural sources of this alkaloid within the genus. In this paper we report findings for nine taxa of Murraya.
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We have determined the nucleotide sequence of a 16-kilobase pair (kb) region of DNA on the 5' side of the human embryonic globin gene (epsilon). This sequence, when combined with previously published sequences, gives an uninterrupted sequence of 21 kb extending from approximately 19.5 kb upstream of the epsilon-globin gene to 0.3 kb 3' to its poly(A)-addition site. Computer-assisted analysis of this DNA reveals no large regions of self-homology but it shows the presence of seven members of the Alu family of repeated DNA, two very short members of the Kpn family of repeated DNA, one unusual direct repeat of 39 base pairs, and two potential stem and loop structures. The overall frequencies of mono- and dinucleotides within the 21 kb approximate those found in the total human genome but the distribution of (G + C)-rich regions signal many sequences of interest. The occurrences of some of the polynucleotides and polydinucleotides also differ appreciably from randomness, and the region contains several large stretches of these simple sequences. We found no evidence of strand asymmetry in the region. Homology between the nucleotide sequences of the human epsilon- and G gamma-globin genes extends only 100 base pairs 5' to the genes. One region, about 10 kb upstream of the gene, shows an apparent clustering of unusual sequence features. We discuss our sequence data in relation to the studies by others of DNAase hypersensitive sites and 5' transcription endpoints in this part of the beta-globin gene cluster.
We have mapped the distribution of the major and minor DNase I-hypersensitive sites in the human "beta-like-globin" gene domain. The minor DNase I-hypersensitive sites map close to the 5' end of each of the beta-like-globin genes. Their presence is specifically associated with the transcription of the immediate downstream beta-like-globin genes. The major DNase I-hypersensitive sites map in what appear to be the 5' and 3' boundary areas of the human beta-like-globin gene domain, a region estimated to span at least 90 kilobases of DNA. These major sites are present in various erythroid cells, which express predominantly either the embryonic, the fetal, or the adult beta-like-globin genes, and seem to be involved in defining the active beta-like-globin genes domain in cells of erythroid lineage. The four major DNase I-hypersensitive sites in the 5' boundary area, when correlated with sequencing data, are shown to be located in DNA regions containing enhancer core-like sequences and alternating purine and pyrimidine bases.
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In an attempt to establish a relationship between proton pumping and the photocycle intermediates of bacteriorhodopsin, we have studied the effects of pH and temperature on flash-induced proton pumping and the photointermediates O640 and M412. The relative quantum yield of flash-induced proton pumping is both pH and temperature dependent. It is high in the acid pH range and at low temperatures but decreases in the basic pH range and at high temperatures. The decay of M412 is biphasic. The amplitude of the slowly decaying component (Ms) was found to be pH dependent with a pK similar to that of the delta pH. The pH dependence of the fast-decaying component (Mf) is opposite to that of Ms and delta pH. Like that of Ms, the amplitude of O640 is high in the acid pH range, but unlike the amplitude of Ms, it declines very rapidly at pHs greater than 6.5; the amplitude of O640 becomes zero around pH 8. The temperature dependence of the amplitude of Ms was found to be similar to that of delta pH, being high at low temperatures and low in the high-temperature range. The temperature dependence of Mf and O640 is opposite to that of delta pH and Ms. Whereas, O640 and Ms seem to be likely candidates (from the pH dependence) for coupling between proton pumping and the photocycle, Ms is more likely because (i) the relative quantum yield of both Ms and delta pH seem not to go to zero at higher pHs and (ii) Ms and delta pH have similar temperature dependence.
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