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81.
82.
Summary Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentration of the selective agent, methotrexate (MTX), was gradually elevated. In mammalian cells, this procedure frequently results in MTX-resistant mutants due to amplification of the gene coding for dihydrofolate reductase (DHFR), the target protein of MTX.Five suspension lines were isolated, with degrees of resistance ranging from 10 to 500 M MTX (in wild type the LD99.9 is 0.2 M). MTXR phenotypes were unstable, as manifested by the loss of resistance upon prolonged growth in the absence of drug. All of the mutants also exhibited high values of MTX-binding protein (60- to 400-fold higher than that of the wild type), which declined to intermediate values upon MTX withdrawal. Finally, cellular extracts from all of the mutants also showed high specific staining of DHFR-activity in gels.The results suggest that the resistance of MTX in these plant cell-lines is mediated by the elevation of the amounts of DHFR, probably as a consequence of gene amplification. 相似文献
83.
Isolation and complete nucleotide sequence of the gene for bovine parathyroid hormone 总被引:7,自引:0,他引:7
The structure of the bovine parathyroid hormone (PTH) gene has been analyzed by Southern blot hybridization of genomic DNA and by nucleotide sequence analysis of a cloned PTH gene. In the Southern analysis, several restriction enzymes produced single fragments that hybridized to PTH cDNA suggesting that there is a single bovine PTH gene. The restriction map of the cloned gene is the same as that determined by Southern blot analysis of bovine DNA. The sequence of 3154 bp of the cloned gene has been determined including 510 bp and 139 bp in the 5' and 3' flanking regions, respectively. The gene contains two introns which separate three exons that code primarily for: (i) the 5' untranslated region, (ii) the pre-sequence of preProPTH, and (iii) PTH and the 3' untranslated region. The gene contains 68% A + T and unusually long stretches of 100- to 150-bp sequences containing alternating A and T nucleotides in the 5' flanking region and intron A. The 5' flanking region contains two TATA sequences, both of which appear to be functional as determined by S1 nuclease mapping. Compared to the rat and human genes, the locations of the introns are identical but the sizes differ. Comparable human and bovine sequences in the flanking regions and introns are about 80% homologous. 相似文献
84.
85.
Karl Ekwall Michèle Kermorgant Geneviève Dujardin Olga Groudinsky Piotr P. Slonimski 《Molecular & general genetics : MGG》1992,233(1-2):136-144
Summary We have characterized the nuclear geneNAM8 inSaccharomyces cerevisiae. It acts as a suppressor of mitochondrial splicing deficiencies when present on a multicopy plasmid. The suppressed mutations affect RNA folding and are located in both group I and group II introns. The gene is weakly transcribed in wildtype strains, its overexpression is a prerequisite for the suppressor action. Inactivation of theNAM8 gene does not affect cell viability, mitochondrial function or mitochondrial genome stability. TheNAM8 gene encodes a protein of 523 amino acids which includes two conserved (RNP) motifs common to RNA-binding proteins from widely different organisms. This homology with RNA-binding proteins, together with the intronic location of the suppressed mitochondrial mutations, suggests that the NAM8 protein could be a non-essential component of the mitochondrial splicing machinery and, when present in increased amounts, it could convert a deficient intron RNA folding pattern into a productive one. 相似文献
86.
Thomas W. Becker Michel Caboche Elisa Carrayol Bertrand Hirel 《Plant molecular biology》1992,19(3):367-379
87.
Adelheid Gauly Alfred Batschauer Albrecht von Arnim Hans Kössel 《Plant molecular biology》1992,19(2):277-287
88.
89.
A biochemical genetic study of the enzyme malate dehydrogenase (MDH) was conducted in the grasshopperOxya j. japonica. Analysis of MDH electrophoretic variation in this species of grasshopper shows that one of the two autosomal loci for MDH in grasshoppers, the Mdh-2 locus, controlling the anodal set of MDH isozymes, is duplicated. Results of breeding studies confirm this and the observed polymorphism at theMdh-2 locus in the two populations ofOxya j. japonica studied can be attributed to three forms of linked alleles at the duplicated locus in equilibrium in both populations. In this respect, all individuals of this species possess heterozygous allelic combinations at the duplicatedMdh-2 locus, which may account for the spread of the duplicated locus in the populations of this species of grasshopper.This research was supported by a grant (Vote F) from the University of Malaya, Kuala Lumpur. 相似文献
90.
C. Stephenson M. Brivet M. Gautier J. Deschatrette R. Gitzelmann P. Karran 《Biochemical genetics》1991,29(3-4):135-144
Expression of the enzymes galactokinase, thymidine kinase, and O6-methylguanine-DNA methyltransferase is occasionally coordinately regulated in human cell lines. We have measured the activities
of these three enzymes in extracts of fibroblasts from individuals with hereditary galactokinase deficiency. These cells do
not express measurable galactokinase activity. The levels of O6-methylguanine-DNA methyltransferase were in the normal range in cells from three galactokinase-deficient individuals. The
activity of thymidine kinase in the affected cells was in the normal range for two of the three individuals. The reduced thymidine
kinase activity in the third individual reflected the extremely poor growth of the cells in culture. Immortalization of one
galactokinase-deficient cell line resulted in loss of O6-methylguanine-DNA methyltransferase activity, but the galactokinase and thymidine kinase levels remained unchanged. The data
indicate that the loss of galactokinase activity in these individuals is the consequence of an alteration of gene expression
which does not involve coordinate silencing with the thymidine kinase and methyltransferase loci. 相似文献