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1.
Polyamine synthesis in rapidly growing tissues   总被引:5,自引:0,他引:5  
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Collagen and noncollagen protein synthesis in cultured human skin fibroblasts was studied in relation to different growth phases. In order to quantify collagen synthesis, we determined the release of incorporated radioactivity using purified bacterial collagenase. Collagen as well as noncollagen protein synthesis markedly decreased during fibroblast growth. On the other hand, we found a 3-fold increase in relative collagen synthesis (i.e. collagen synthesis compared to total protein synthesis) comparing cells in the log growth phase with cells in the stationary growth phase.  相似文献   

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Anomalous synthesis of ppGpp in growing cells.   总被引:13,自引:0,他引:13  
J Gallant  L Palmer  C C Pao 《Cell》1977,11(1):181-185
In E. coli cells, accumulation of ppGpp is normally triggered by conditions that restrict the aminoacylation of tRNA or interfere with carbon/energy source metabolism; in both cases, the nucleotide's accumulation is associated with control of stable RNA synthesis and is generally believed to bring it about. We have found an anomalous situation wherein vigorously growing cells accumulate a high level of ppGpp and there is no restriction of stable RNA synthesis. This occurs when wild-type cells are shifted up from an abnormally low growth temperature to one in the optimal range (35 degrees C-40 degrees C). The effect is partly, but not entirely, dependent upon the presence of a functional relA gene product. These results appear to call into question the simpler interpretations of the role of ppGpp in the control of stable RNA synthesis.  相似文献   

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Spohn  Marie 《Biogeochemistry》2020,147(3):225-242

Despite the importance of phosphorus (P) as a macronutrient, the factors controlling the pool sizes of organic and inorganic P (OP and IP) in soils are not yet well understood. Therefore, the aim of this study was to gain insights into the pools sizes of OP, IP and organic carbon (OC) in soils and soil particle size fractions. For this purpose, I analyzed the distribution of OP, IP, and OC among particle size fractions depending on geographical location, climate, soil depth, and land use, based on published data. The clay size fraction contained on average 8.8 times more OP than the sand size fraction and 3.9 and 3.2 times more IP and OC, respectively. The OP concentrations of the silt and clay size fraction were both negatively correlated with mean annual temperature (R2 = 0.30 and 0.31, respectively, p < 0.001). The OC:OP ratios of the silt and clay size fraction were negatively correlated with latitude (R2 = 0.49 and 0.34, respectively, p < 0.001). Yet, the OC:OP ratio of the clay size fraction changed less markedly with latitude than the OC:OP ratio of the silt and the sand size fraction. The OC concentrations of all three particle size fractions were significantly (p < 0.05) lower in soils converted to cropland than in adjacent soils under natural vegetation. In contrast, the OP concentration was only significantly (p < 0.05) decreased in the sand size fraction but not in the other two particle size fractions due to land-use change. Thus, the findings suggest that OP is more persistent in soil than OC, which is most likely due to strong sorptive stabilization of OP compounds to mineral surfaces.

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Growing season length can control plant size over altitudinal and biogeographic scales, but its effect at the scale of meters is largely unexplored. Within the riparian zone of a northern California river, scarlet monkeyflower, Mimulus cardinalis , grows significantly larger at sites high in the channel as compared to sites low in the channel, and even larger where tributaries meet the main stem of the river. We explored the hypothesis that markedly different growing season length controls this size variation. Due to the very gradual retreat of the water level following winter flooding, emergence time is three months longer for plants growing at tributary confluences than for plants growing at low elevations in the channel. Consistent with the growing season length hypothesis, we found no difference in transplant growth between river and tributary confluence sites in an experiment where we equalized growing season length at these locations. Moreover, a second experiment showed that individuals planted earlier in the year gain a distinct size advantage over those planted later, even though growing conditions are less ideal. These results suggest that emergence time may be a key determinant of plant size structure along rivers, an important result considering forecasted variation in water flows with climate change.  相似文献   

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Log growth Tetrahymena pyriformis GL were deciliated by means of a calcium pulse and allowed to regenerate their cilia in a non-nutrient recovery medium. Polyribosome profiles show only small amounts of polysomes up to 30 min after suspension in recovery medium. After this time the number of polysomes increases continuously as protein synthetic activity and motility are recovered. Labeling of whole cells with l-[35S]methionine and comparison of the resulting electrophoretic patterns reveals a marked induction of tubulin synthesis as cilia regeneration proceeds. At its peak, tubulin accounts for 7–10% of the incorporated label but this peak occurs 35 min after the cells become greater than 90% motile and about 25 min after the cilia reach full length. These results are discussed with respect to the regulatory mechanism of tubulin induction and induction of tubulin synthesis in starved Tetrahymena.  相似文献   

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Immunochemical techniques were used to study the mechanism underlying the marked increase in the level of acetyl-coenzyme A carboxylase activity in chick liver observed after hatching. The results of immunochemical titrations and Ouchterlony double-diffusion analysis indicated that this increase in the activity level of the enzyme was due to an elevation in the enzyme quantity. Isotopic leucine incorporation studies revealed that the rate of synthesis of the enzyme per liver was 18-fold higher in 9-day-old chicks than in 1-day-old chicks. In terms of the synthesis rate per gram of liver, this increase was 5-fold. The half-life for degradation of the enzyme in 9-day-old chicks was shown to be 46 h, whereas no apparent degradation of the enzyme as well as of total soluble liver protein was observed in 1-day-old chicks. These results indicate that the increase in the hepatic acetyl-CoA carboxylase content in growing chicks can be ascribed to accelerated synthesis of the enzyme.  相似文献   

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