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101.
Ellen M. Johnson Linda S. Schnabelrauch Barbara B. Sears 《Molecular & general genetics : MGG》1991,225(1):106-112
Summary A bovine tRNA gene cluster has been characterized and the sequences of four tDNAs determined. Two of the tDNAs could encode tRNASer
IGA, one tDNASer
UGA, and the fourth tRNAGln
CUG. The three serine tDNAs representing the UCN codon isoacceptor family are almost identical. However, the sequence of the tDNASer
TGA differs from a previously sequenced bovine tDNASer
TGA at 12 positions (ca. 14%). This finding suggests that in the bovine genome, two subfamilies of genes might encode tRNASer
UGA. It also raises the possibility that new genes for a specific UCN isoacceptor might arise from the genes of a different isoacceptor, and could explain previously observed differences between species in the anticodons of coevolving pairs of tRNAsSer
UCN. The gene cluster also contains complete and partial copies, and fragments, of the BCS (bovine consensus sequence) SINE (short interspersed nuclear element) family, six examples of which were sequenced. Some of these elements occur in close proximity to two of the serine tDNAs. 相似文献
102.
Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria 总被引:4,自引:0,他引:4
Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The 13C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (13C between-25.3 and-27.8) were significantly less depleted in 13C than needles (13C between-27.3 and-29.1), and 13C in twigs increased consistently with age. The 15N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles 15N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in 15N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. 15N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. 15N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The 15N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed. 相似文献
103.
Iron-efficient (WF9 corn and Coker 227 oat) and Fe-inefficient (ys1 corn and TAM 0–312 oat) cultivars were comparatively tested for their response to Fe-deficiency stress induced by the use of either ferrous or ferric chelators. Corn and oats were grown in 20 M Fe with 0, 60, and 120 M BPDS and 40 M Fe with 0, 120, and 240 M BPDS and 20 M Fe with 0 and 40 M EDDHA. All four cultivars tested, both Fe-efficient and Fe-inefficient, continuously reduced Fe3+ to Fe2+ at a low level as evidenced by the production of Fe2+ (BPDS)3 in test nutrient solutions over time. Severity of chlorosis increased as more BPDS was added to the nutrient solutions for both WF9 and ys1 corn, but unlike corn, Coker 227 and TAM 0-312 oats were both able to obtain Fe from the Fe2+ (BPDS)3 complex and were less chlorotic as a result. In short-term (4-hour) in vivo measurements, iron-stressed WF9 (Fe-efficient) corn reduced more Fe3+ to Fe2+ than similarly stressed ys1 corn, Coker 227 oat or TAM 0-312 oat. Thus, at the same time that Fe-efficient WF9 corn reduces more Fe than the other cultivars, it is also unable to compete with BPDS for that Fe in the nutrient solution. These differences coupled with the observation that only Coker 227 oat produced measureable iron solubilizing substances (phytosiderophores) suggest that these two species differ in their mechanisms for obtaining Fe during Fe-deficiency stress. 相似文献
104.
Ayumi Ohsaki Yoshihisa Kasetani Yukihiro Asaka Kozo Shibata Takashi Tokoroyama Takashi Kubota 《Phytochemistry》1991,30(12):4075-4077
Three trans-clerodane diterpenoids, pilosanol A, B and C, the last compound being a glucoside, have been isolated from the roots of Portulaca pilosa. They show a marked contrast in skeletal type with the constituents of aerial part. Evolutionary changes in the biosynthetic abilities of Portulaca species is discussed. 相似文献
105.
Maria Ransjö 《Bioscience reports》1991,11(4):203-211
The protein kinase C-(PKC) activating phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA; 100 nmol/l) and phorbol 12, 13-dibutyrate (PDBU; 100 nmol/l) enhanced basal cyclin AMP accumulation in cultured neonatal mouse calvaria. The cyclic AMP response to parathyroid hormone (PTH; 10 nmol/l) and the adenylate cyclase activators forskolin (1–3 mol/l) and choleratoxin (0.1 mg/ml) was potentiated in a more than additive manner by TPA and PDBU. In contrast, phorbol 13-monoacetate (phorb-13; 100 nmol/l), a related compound but inactive on PKC, had no effect on basal or stimulated cyclic AMP accumulation. In the presence of indomethacin (1mol/l), TPA and PDBU had no effect on cyclic AMP accumulation in calvarial bones per se, but were still able to cause a significant enhancement of the response to PTH, forskolin and choleratoxin. PTH-, forskolin- and choleratoxin-stimulated cyclic AMP accumulation in rat osteosarcoma cells UMR 106-01 was synergistically potentiated by TPA and PDBU, but not by phorb.-13. These data indicate that PKC enhances cyclic AMP formation and that the level of interaction may be at, or distal to, adenylate cyclase. 相似文献
106.
Summary A simple E.COSY type technique is described for measurement of two-bond JCOH coupling constants in proteins that are uniformly enriched with13C. The method has been used to measure2JCOH for 132 residues in the proteins calmodulin and staphylococcal nuclease having non-overlapping H–C correlations. Measured2JCOH coupling constants fall in the 0 to –9.5 Hz range. A separate experiment, measuring the accuracy of these values, indicates a root-mean-square error of 1 Hz. Comparison of the J couplings with the dihedral back bone angles from crystallographic studies confirms a weak but statistically significant correlation between the dihedral angle and the magnitude of2JCOH, but also indicates that parameters other than have a significant effect on the value of the coupling. 相似文献
107.
The effects of lithium (Li+) on the adenylyl cyclase and inositol phospholipid receptor signalling pathways were compared directly in noradrenergic and carbachol stimulated rat brain cortical tissue slices. Li+ was a comparatively weak inhibitor of noradrenaline-stimulated cyclic AMP accumulation with an IC50 of approx. 20 mM. By contrast, half-maximal effects of Li+ on inositol monophosphate (InsP) accumulation in [3H]inositol labelled tissue slices occurred at about 1 mM. A similar IC50 for Li+ of about 1 mM was also obtained for noradrenaline-stimulated accumulation of CMP-phosphatidate (CMPPA), a sensitive indicator of intracellular inositol depletion, in tissue slices that had been prelabelled with [3H]cytidine. The effect of myo-inositol (inositol) depletion on the prolonged activity of phosphoinositidase C (PIC) was examined in carbachol-stimulated corticol slices using a novel mass assay fro InsP. Exposure to a maximal dose of carbachol for 30 min in the presence of 5 mM Li+ caused a 10-fold increase in the level of radioactivity associated with the InsP fraction, but only a 2-fold increase in InsP mass. During prolonged incubations in the presence of both carbachol and Li+ the accumulation of InsP mass was enhanced if 30 mM inositol was included in the medium. The results are comptable with the inositol depletion hypothesis of Li+ action but do not support the concept that adenylyl cyclase or guanine nucleotide dependent proteins represent therapeutically relevant targets of this drug. 相似文献
108.
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