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991.
992.
In natural populations of the anaerobic phototrophic bacterium Chromatium weissei, many cells support a prokaryotic epibiont. This epibiont appears in several forms, all from the life cycle of a single species. A typical epibiont consists of one to five flattened coccoid cells stacked one above the other, perpendicular to the C. weissei surface. The cells at the proximal and distal ends of the stack are 0.6 m in diameter and 0.8 m in length; mid-stack cells are slightly shorter. A typical three or four cell stack is 2 m in length. Small mesosome-like inclusions in the distal cell are involved in the development of droplet shaped cells which are released from the end of each stack. These specialised droplet cells probably transfer to new hosts when C. weissei cells collide, thereafter developing into new epibiont stacks. It is likely that the epibiont grows heterotrophically using the substantial production of dissolved organic carbon within the dense plates of photosynthesising C. weissei which develop naturally. Thus the epibiont uses its unusual method of growth and dispersion to maintain position in the microbial plate upon which it depends.  相似文献   
993.
We have isolated and sequenced a MAP (mitogen-activated protein) kinase-type cDNA from a tobacco (Nicotiana tabacum L.) cell suspension cDNA library by screening with a PCR fragment amplified from the same library with oligonucleotide primers corresponding to two sequences conserved in yeast and animal MAP kinases. The tobacco sequence, ntf3, shows 45–54% identity to various members of the MAP kinase family at the protein level. Northern experiments showed that ntf3 is expressed in all tobacco tissues tested, including pollen isolated at different developmental stages. Southern analysis indicated that, as in other organisms, there is a family of MAP kinase genes in tobacco. In complementary tests, ntf3 could not substitute the yeast MAP kinase genes fus3 and kss1.  相似文献   
994.
Summary We used electron microscopical techniques to study ultrastructural changes during the acquisition of embryogenic competence in immature pollen grains ofNicotiana tabacum, isolated at the early- or mid-bicellular stage and cultured in vitro under starvation conditions. Cytoplasmic and nuclear changes during the starvation treatment are reported. Dedifferentiation of plastids, dilation of the wall of the generative cell, the appearance of a large vacuole, loss of nuclear pores in the vegetative nucleus, changes in chromatin and nucleolar structure, and a decrease in the size of the nucleolus were observed. We suggest that these events are the first step in the switch from generative to vegetative generation during pollen embryogenesis.  相似文献   
995.
Four novel mutations are identified in the ornithine transcarbamylase (OTC) gene, in four patients with OTC deficiency (an X-linked disorder). The mutations represent three different categories: missense (Ile159Thr and Ala209Val), nonsense (Tyr167Stop), and causing inefficient splicing (GA in the first intronic base) with associated aberrant splicing. They are located in exons 5, and 6, and in intron 3. Two of the mutations arose de novo in the patients, and only one mutation occurs at a CpG site. The nonsense and the splicing mutation cause, respectively, lethal early onset and non-lethal, delayed early onset clinical presentations in males. Our results confirm for Spain the high genotypic heterogeneity of OTC deficiency.  相似文献   
996.
We have isolated the ypfP gene (accession number P54166) from genomic DNA of Bacillus subtilis Marburg strain 60015 ( Freese and Fortnagel, 1967 ) using PCR. After cloning and expression in E. coli , SDS–PAGE showed strong expression of a protein that had the predicted size of 43.6 kDa. Chromatographic analysis of the lipids extracted from the transformed E. coli revealed several new glycolipids. These glycolipids were isolated and their structures determined by nuclear magnetic resonance (NMR) and mass spectrometry. They were identified as 3-[ O -β- D -glucopyranosyl-(1→6)- O -β- D -glucopyranosyl]-1,2-diacylglycerol, 3-[ O -β- D -glucopyranosyl-(1→6)- O -β- D -glucopyranosyl-(1→6)- O -β- D -glucopyranosyl]-1,2-diacylglycerol and 3-[ O -β- D -glucopyranosyl-(1→6)- O -β- D -glucopyranosyl-(1→6)- O -β- D -glucopyranosyl-(1→6)- O -β- D -glucopyranosyl]-1,2-diacylglycerol. The enzymatic activity expected to catalyse the synthesis of these compounds was confirmed by in vitro assays with radioactive substrates. In these assays, one additional glycolipid was formed and tentatively identified as 3-[ O -β- D -glucopyranosyl]-1,2-diacylglycerol, which was not detected in the lipid extract of transformed cells. Experiments with some of the above-described glycolipids as 14C-labelled sugar acceptors and unlabelled UDP-glucose as glucose donor suggest that the ypfP gene codes for a new processive UDP-glucose: 1,2-diacylglycerol-3-β- D -glucosyl transferase. This glucosyltransferase can use diacylglycerol, monoglucosyl-diacylglycerol, diglucosyldiacylglycerol or triglucosyldiacylglycerol as sugar acceptor, which, apart from the first member, are formed by repetitive addition of a glucopyranosyl residue in β (1→6) linkage to the product of the preceding reaction.  相似文献   
997.
The degree of genetic variability in the hypervariable region 1 of hepatitis C virus (HCV) was analyzed by cloning and sequencing HCV genomes obtained in paired samples of serum, liver tissue, and peripheral blood mononuclear cells (PBMC) from four chronic hepatitis C patients. Genetic variability in serum was higher than in liver tissue or PBMC at the level of complexity (the number of different sequences obtained from each type of tissue) as well as at the level of genetic distance between all pairs of sequences within each tissue (compared by the Student t test; P < 0.001 for two patients and P < 0.01 for another). The spectrum of viral genomes differed among the three types of tissue, as shown by segregation of sequences according to their tissue of origin in phylogenetic analysis and by statistical analysis of mean genetic distances observed between sequences obtained from different tissues (P < 0.001), but sequences from liver tissue and PBMC were more closely related to each other than to those from serum.  相似文献   
998.
Viña, José, Emilio Servera, Miguel Asensi, JuanSastre, Federico V. Pallardó, José A. Ferrero, JoséGarcía-de-la-Asunción, Vicente Antón, and JulioMarín. Exercise causes blood glutathione oxidation inchronic obstructive pulmonary disease: prevention by O2therapy. J. Appl. Physiol. 81(5):2199-2202, 1996.The aim of the present study was to determinewhether glutathione oxidation occurs in chronic obstructive pulmonarydisease (COPD) patients who perform exercise and whether this could beprevented. Blood glutathione red-ox ratio [oxidized-to-reducedglutathione (GSSG/GSH)] was significantly increased when patientsperformed exercise for a short period of time until exhaustion. Theirresting blood GSSG/GSH was 0.039 ± 0.008 (SD)(n = 5), whereas after exercise itincreased to 0.085 ± 0.019, P < 0.01. Glutathione oxidation associated with exercise was partiallyprevented by oxygen therapy (resting value: 0.037 ± 0.014, n = 5; after exercise: 0.047 ± 0.016, n = 5, P < 0.01). We conclude that lightexercise causes an oxidation of glutathione in COPD patients, which canbe partially prevented by oxygen therapy.

  相似文献   
999.
Activation of carbamoyl phosphate synthetase by cryoprotectants   总被引:1,自引:0,他引:1  
Molecular and Cellular Biochemistry - Carbamoyl phosphate synthetase I (E.C.6.3.4.16) from rat liver is activated by a range of cryoprotectants. Their diverse chemical structure and the normal...  相似文献   
1000.
We studied the anterior pituitary function in 36 patients (25 females and 11 males, mean age: 35 years) with untreated Cushing's syndrome by simultaneous triple stimulus with insulin, TRH and LHRH. Thirty-one patients (86%) had Cushing's disease and five (14%) had an adrenal adenoma. We observed a lack of response of GH to hypoglycemia in 88%, TSH to TRH in 91%, LH to LHRH in 30%, FSH to LHRH in 12% and PRL to TRH in 6% of the patients. Low-to-normal total thyroxine (T4) values were obtained in 37%, with low triiodothyronine levels in 87%. The free-T4 index was normal in all patients. Total testosterone was low in only one adult man, while estradiol and progesterone were low in 45% and 15% of premenopausal women, respectively. We observed no differences in either axis among patients with Cushing's syndrome of different etiologies. Nor was there any statistical difference between the frequency of alteration of each axis and the levels of urinary free cortisol or the duration of the disease. We conclude that hypercortisolism is responsible for the abnormalities in anterior pituitary function in Cushing's syndrome.  相似文献   
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