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Amino acid replacements resulting from super-suppression of nonsense mutants of iso-1-cytochrome c from yeast 总被引:25,自引:0,他引:25
The eight class I, set 1 super-suppressor genes, SUP2, SUP3, SUP4, SUP5, SUP6, SUP7, SUP8 and SUP11 are not closely linked and map at distinct loci throughout the genome of yeast. Each of these suppressors causes the production of 5 to 10% of the normal amount of iso-1-cytochrome c when it is individually coupled to the ochre (UAA) mutant cy1-2. All eight iso-1-cytochromes c contain a residue of tyrosine at position 20 which corresponds to the site of the ochre codon. Several of these super-suppressors also were shown to act on cy1-9, but at a much lower efficiency. It was shown that iso-1-cytochrome c from one of the suppressed cy1-9 strains contains a tyrosine at position 2, which corresponds to the site of the ochre codon in this mutant. It is suggested that the gene product of the eight super-suppressors is tyrosine transfer RNA. 相似文献
997.
D Vuitton R Eloy J Dauchel M Klein J F Grenier 《Comptes rendus des séances de la Société de biologie et de ses filiales》1976,170(1):187-193
The ability of the liver to reduce the intensity of the graft versus host (GVH) reaction has been investigated in F1 hybrid rats implanted with parental lymph nodes. Intrahepatic and intrarenal tissue implantations were compared using classical GVH criteria. The intrahepatic implantation of lymph nodes suppress the mortality observed after intrarenal implantation. The results confirm the interest of portal drainage in organ transplantation and suggest a new site of implantation for lymphoid cells. 相似文献
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Affinity labeling studies of NADP(+)-glutamate dehydrogenase from Salmonella typhimurium have shown that the peptide Leu-282-Lys-286 is located near the coenzyme site [Haeffner-Gormley et al. (1991) J. Biol. Chem. 266, 5388-5394]. The present study was undertaken to evaluate the role of lysine-286. The mutant enzymes K286R, K286Q, and K286E were prepared by site-directed mutagenesis, expressed in Escherichia coli, and purified. The Vmax values (micromoles of NADPH per minute per milligram of protein) were similar for WT (270), K286R (529), K296Q (409), and K286E (382) enzymes. As measured at pH 7.9, the Km value for NADPH was much greater for K286E (280 microM) than for WT (9.8 microM), K286R (30 microM), or K286Q (66 microM) enzymes. The efficiencies (kcat/Km) of the WT and K286R mutant were similar (1.2 x 10(3) min-1 microM-1 and 1.0 x 10(3) min-1 microM-1, respectively) while those of K286Q (0.30 x 10(3) min-1 microM-1) and K286E (0.07 x 10(3) min-1 microM-1) were greatly reduced. The decreased efficiency of the K286E mutant results from the increase in Km-NADPH, consistent with a role for a basic residue at position 286 which enhances the binding of NADPH. Plots of Vmax vs pH showed the pH optima to be 8.1-8.3 for all enzymes at saturating NADPH concentrations. A 40-fold increase in Km-NADPH for K286E was observed as the pH increased from 5.98 to 8.08, from which a unique pKe of 6.5 was calculated.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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