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941.
The extremely thermophilic, obligately aerobic bacterium Sulfolobus solfataricus forms the tetrapyrrole precursor, -aminolevulinic acid (ALA), from glutamate by the tRNA-dependent five-carbon pathway. This pathway has been previously shown to occur in plants, algae, and most prokaryotes with the exception of the -group of proteobacteria (purple bacteria). An alternative mode of ALA formation by condensation of glycine and succinyl-CoA occurs in animals, yeasts, fungi, and the -proteobacteria. Sulfolobus and several other thermophilic, sulfur-dependent bacteria, have been variously placed within a subgroup of archaea (archaebacteria) named crenarchaeotes, or have been proposed to comprise a distinct prokaryotic group designated eocytes. On the basis of ribosomal structure and certain other criteria, eocytes have been proposed as predecessors of the nuclear-cytoplasmic descent line of eukaryotes. Because aplastidic eukaryotes differ from most prokaryotes in their mode of ALA formation, and in view of the proposed affiliation of eocytes to eukaryotes, it was of interest to determine how eocytes form ALA. Sulfolobus extracts were able to incorporate label from [1-14C]glutamate, but not from [2-14C]glycine, into ALA. Glutamate incorporation was abolished by preincubation of the extract with RNase. Sulfolobus extracts contained glutamate-1-semialdehyde aminotransferase activity, which is indicative of the five-carbon pathway. Growth of Sulfolobus was inhibited by gabaculine, a mechanism-based inhibitor of glutamate-1-semialdehyde aminotransferase, an enzyme of the five-carbon ALA biosynthetic pathway. These results indicate that Sulfolobus uses the five-carbon pathway for ALA formation.Abbreviations AHA
4-amino-5-hexynoic acid
- ALA
-aminolevulinic acid, Gabaculine, 3-amino-2,3-dihydrobenzoic acid
- GSA
glutamate 1-semialdehyde 相似文献
942.
K. Bender R. T. Seibert T. F. Wienker V. Kren M. Pravenec S. Bissbort 《Biochemical genetics》1994,32(5-6):147-154
A genetic locus controlling the electrophoretic mobility of a methylglyoxal dehydrogenase (EC 1.2.1.23) in the rat is described. The locus, designatedMgd1, is expressed in liver and kidney. Inbred rat strains have fixed either alleleMgd1
a
or alleleMgd1
b
. Codominant expression is observed in heterozygotes, providing evidence for a tetrameric enzyme structure. Backcross progenies showed the expected 1:1 segregation ratio, and there is evidence thatMgd1 is linked toPep3 andFh1 on chromosome 13. There is also evidence for two additional methylglyoxal dehydrogenases:Mgd2, present in liver and kidney, andMgd3, present only in heart.Supported by the Deutsche Forschungsgemeinschaft (Grant Be 352/18-1). 相似文献
943.
Hans-Jochen Schfer Gabriele Rathgeber Achim Schuhen Richard J. Berzborn 《FEBS letters》1994,340(3):265-268
UV irradiation of the ATPase (CF1) from spinach chloroplasts in the presence of 3'-arylazido-β-alanyl-8-azido ATP (8,3'-DiN3ATP) results in a nucleotide-dependent inactivation of the enzyme and in a nucleotide-dependent formation of -β cross-links. The results demonstrate an interfacial localization of the nucleotide binding sites on CF1. 相似文献
944.
Jan Kwiatowski Douglas Skarecky Kevin Bailey Francisco J. Ayala 《Journal of molecular evolution》1994,38(5):443-454
The phylogeny and taxonomy of the drosophilids have been the subject of extensive investigations. Recently, Grimaldi (1990)
has challenged some common conceptions, and several sets of molecular data have provided information not always compatible
with other taxonomic knowledge or consistent with each other. We present the coding nucleotide sequence of the Cu,Zn superoxide
dismutase gene (Sod) for 15 species, which include the medfly Ceratitis capitata (family Tephritidae), the genera Chymomyza and Zaprionus, and representatives of the subgenera Dorsilopha, Drosophila, Hirtodrosophila, Scaptodrosophila, and Sophophora. Phylogenetic analysis of the Sod sequences indicates that Scaptodrosophila and Chymomyza branched off the main lineage before the major Drosophila radiations. The presence of a second intron in Chymomyza and Scaptodrosophila (as well as in the medfly) confirms the early divergence of these two taxa. This second intron became deleted from the main
lineage before the major Drosophila radiations. According to the Sod sequences, Sophophora (including the melanogaster, obscura, saltans, and willistoni species groups) is older than the subgenus Drosophila; a deep branch splits the willistoni and saltans groups from the melanogaster and obscura groups. The genus Zaprionus and the subgenera Dorsilopha and Hirtodrosophila appear as branches of a prolific “bush” that also embraces the numerous species of the subgenus Drosophila. The Sod results corroborate in many, but not all, respects Throckmorton's (King, R.C. (ed) Handbook of Genetics. Plenum Press, New York, pp. 421–469, 1975) phylogeny; are inconsistent in some important ways with Grimaldi's (Bull. Am. Museum Nat. Hist.
197:1–139, 1990) cladistic analysis; and also are inconsistent with some inferences based on mitochondrial DNA data. The Sod results manifest how, in addition to the information derived from nucleotide sequences, structural features (i.e., the deletion
of an intron) can help resolve phylogenetic issues.
Correspondence requests to: F. J. Ayala 相似文献
945.
The effects of human red cell glycophorin A (GPA) on the translocation to the plasma membrane and anion transport activity of the human erythrocyte anion transporter (band 3; AE1) have been examined using the Xenopus oocyte expression system. We show that band 3 accumulates steadily at the oocyte surface with time in the presence or absence of GPA, but this occurs more quickly when GPA is coexpressed. The amount of band 3 at the surface is determined by the concentrations of band 3 and GPA cRNA that are injected, with a higher proportion of total band 3 being translocated to the surface in the presence of GPA cRNA. The increased expression of DNDS-sensitive chloride transport is highly specific to GPA, and is not observed when the cRNA to the putative glycophorin E or a very high concentration of the cRNA to glycophorin C are coexpressed with band 3 in oocytes.We thank Dr. Kay Ridgwell and Charlotte Ratcliffe for supplying plasmids and Dr. David Anstee for antibodies. This work was supported by grants from the Medical Research Council. 相似文献
946.
A human episomal sequence (HALF1) has been identified by its ability to restore expression of hepatic functions when used to transfect a rat dedifferentiated cell line. The genomic equivalent of this human episome (gHALF1) and its flanking sequences were analyzed. HALF1 itself does not present the characteristics of a transposable element but half of its sequence corresponds to retroposons, including Alu and L1 repeats and a processed pseudogene, known to transposevia RNA intermediates. The structural characteristics of these different kinds of retroposons and their origin and evolution were analyzed. 相似文献
947.
Gabriel Gutiérrez Josep Casadesús Jose L. Oliver Antonio Marine 《Journal of molecular evolution》1994,39(4):340-346
E. coli genes that contain a high frequency of the tetranucleotide CTAG are also rich in the tetramers CTTG, CCTA, CCAA, TTGG, TAGG, and CAAG (group-I tetramers). Conversely, E. coli genes lacking CTAG are rich in the tetranucleotides CCTG, CCAG, CTGG, and CAGG (group-II tetramers). These two gene samples differ also in codon usage, amino acid composition, frequency of Dcm sites, and contrast vocabularies. Group-I tetramers have in common that they are depleted by very-short-patch repair (VSP), while group-II tetramers are favored by VSP activity. The VSP system repairs G:T mismatches to G:C, thereby increasing the overall G+C content of the genome; for this reason the CTAG-rich sample has a lower G+C content than the CTAG-poor sample. This compositional heterogeneity can be tentatively explained by a low level of VSP activity on the CTAG-rich sample. A negative correlation is found between the frequency of group-I tetramers and the level of gene expression, as measured by the Codon Adaptation Index (CAI). A possible link between the rate of VSP activity and the level of gene expression is considered.Correspondence to: A. Marine 相似文献
948.
Evolution of secondary structure in the family of 7SL-like RNAs 总被引:8,自引:0,他引:8
Primate and rodent genomes are populated with hundreds of thousands copies of Alu and B1 elements dispersed by retroposition, i.e., by genomic reintegration of their reverse transcribed RNAs. These, as well as primate BC200 and rodent 4.5S RNAs, are ancestrally related to the terminal portions of 7SL RNA sequence. The secondary structure of 7SL RNA (an integral component of the signal recognition particle) is conserved from prokaryotes to distant eukaryotic species. Yet only in primates and rodents did this molecule give rise to retroposing Alu and B1 RNAs and to apparently functional BC200 and 4.5S RNAs. To understand this transition and the underlying molecular events, we examined, by comparative analysis, the evolution of RNA structure in this family of molecules derived from 7SL RNA.RNA sequences of different simian (mostly human) and prosimian Alu subfamilies as well as rodent B1 repeats were derived from their genomic consensus sequences taken from the literature and our unpublished results (prosimian and New World Monkey). RNA secondary structures were determined by enzymatic studies (new data on 4.5S RNA are presented) and/or energy minimization analyses followed by phylogenetic comparison. Although, with the exception of 4.5S RNA, all 7SL-derived RNA species maintain the cruciform structure of their progenitor, the details of 7SL RNA folding domains are modified to a different extent in various RNA groups. Novel motifs found in retropositionally active RNAs are conserved among Alu and B1 subfamilies in different genomes. In RNAs that do not proliferate by retroposition these motifs are modified further. This indicates structural adaptation of 7SL-like RNA molecules to novel functions, presumably mediated by specific interactions with proteins; these functions were either useful for the host or served the selfish propagation of RNA templates within the host genome.Abbreviations FAM
fossil Alu element
- FLAM
free left Alu monomer
- FRAM
free right Alu monomer
- L-Alu
left Alu subunit
- R-Alu
right Alu subunit
Correspondence to: D. LabudaDedicated to Dr. Robert Cedergren on the occasion of his 25th anniversary at the University of Montreal 相似文献
949.
Jussi-Pekka Usenius Pauli Vainio Juha Hernesniemi † Risto A. Kauppinen 《Journal of neurochemistry》1994,63(4):1538-1543
Abstract: We have studied 14 patients with different grades of astrocytomas using 1 H NMR spectroscopy in vivo. Typically, astrocytomas exhibited a low N -acetyl-aspartate peak, a prominent signal from choline group-containing compounds, and lactate in the 1 H NMR spectra in vivo. The uncorrected choline/creatine + phosphocreatine peak area ratios were higher in tumors than in normal brain tissue. Absolute concentration of choline-containing compounds (1.74 ± 0.09 mmol/L) in the normal brain tissue was not different in any grade of astrocytoma, but total creatine concentration in healthy brain (7.49 ± 0.30 mmol/L) was higher than that in grade IV astrocytomas (4.84 ± 0.89 mmol/L). Relaxation constants of choline-containing compounds did not differ in tumors from those determined in normal brain. Perchloric acid extracts of biopsy samples from 35 astrocytomas and 13 samples of normal temporal white matter were analyzed with 1 H NMR. Total concentration of choline-containing compounds did not differ between controls and any grade of astrocytoma when the quantification was done in vitro. It is interesting that phosphorylcholine concentration was about twofold greater in grade IV astrocytomas than in controls or other grades of astrocytomas. We conclude that high phosphorylcholine in grade IV astrocytomas may be an indicator of degree of malignancy. The proportional changes within the group of choline-containing compounds observed in vitro were not reflected in the NMR properties of choline signal in vivo. 相似文献
950.
Xiao-Ming Zhou Patricia Curran Jesse Baumgold Peter H. Fishman 《Journal of neurochemistry》1994,63(4):1361-1370
Abstract: Exposure of human SK-N-MC neurotumor cells to 4β-phorbol 12-myristate 13-acetate (PMA) increased isoproterenol stimulation of cyclic AMP levels by severalfold. This potentiation was blocked by inhibitors of protein kinase C (PKC) and did not occur in cells in which PKC had been down-regulated. PMA treatment also enhanced the stimulation by dopamine, cholera toxin, and forskolin. Thus, the effect of PMA on the adenylylcyclase system was postreceptor and involved either the guanine nucleotide binding regulatory (G) proteins or the cyclase itself. As PMA treatment did not impair the inhibition of isoproterenol stimulation by neuropeptide Y, an involvement of the inhibitory G protein Gi was unlikely. Cholate extracts of membranes from control and PMA-treated cells were equally effective in the reconstitution of adenylylcyclase activity in S49 cyc? membranes, which lack the stimulatory G protein subunit Gsα; thus, Gs did not appear to be the target of PMA action. Membranes from PMA-treated cells exhibited increased adenylylcyclase activity to all stimulators including Mn2+ and Mn2+ plus forskolin. In addition, activity was increased when control membranes were incubated with ATP and purified PKC from rat brain. This is consistent with a direct effect of PKC on the adenylylcyclase catalyst in SK-N-MC cells. PMA treatment also resulted in a shift to less sensitivity in the Kact for isoproterenol but not for dopamine or CGP-12177 (a β3-adrenergic agonist) stimulation. Thus, the β1 but not the D1 or β3 receptors were being desensitized by PKC activation. Analysis of SK-N-MC cells by western blotting with antibodies against different PKC isozymes revealed that both the α and ζ isozymes were present in these cells. Whereas PKC-α was activated and translocated from cytosol to membrane by phorbol esters, the ζ isozyme was not. Thus, PKC-α, which has been implicated in desensitization in other cell lines, also appears to potentiate adenylylcyclase activity. 相似文献