Differential induction of chromosome puffs in two cell types of Melanagromyza obtusa

The patterns of puffing activity in polytene nuclei of salivary gland (SG) and midgut (MG) tissues of Melanagromyza obtusa have been studied after heat shock (HS), 2-4-dinitrophenol (DNP) or benzamide treatment. This study has revealed that HS and DNP treatments induced the same set of puffs but in a tissue-specific pattern. Benzamide treatment was found ineffective in inducing puffing activity. Some HS genes were also found to be more or less active during normal development, indicating some function in the normal metabolism of the cells.     

Yeast fatty acid synthase: structure to function relationship

The yeast fatty acid synthase is a multifunctional enzyme composed of two nonidentical subunits in an alpha 6 beta 6 complex that is active in synthesizing fatty acids. The seven catalytic activities required for fatty acid synthesis are divided between the alpha and beta subunits such that the alpha 6 beta 6 complex has six complements of each activity. It has been proposed that these are organized into six centers for fatty acid synthesis. There are different opinions regarding the operation of these centers in the alpha 6 beta 6 complex, on view being that they are functionally independent and the other proposes half-sites activity for the complex. We have attempted to distinguish between these proposals by the most direct method of active site titration, i.e., quantitation of fatty acyl product in the absence of turnover. This was accomplished by using p-nitrophenyl thioacetate and thiophenyl malonate (in place of the coenzyme A analogues) as substrates along with NADPH, thereby depriving the yeast synthase of coenzyme A required to release product as fatty acyl coenzyme A. The amount of fatty acyl product formed was quantitated by gas-liquid chromatography, as well as by direct estimation of radioactivity in the product when p-nitrophenyl thio [1-14C] acetate was used as a substrate. In both cases, a stoichiometry of close to six was found for mole of fatty acid synthesized per mole of alpha 6 beta 6 complex. This indicates that there are six functional centers for fatty acid synthesis in the multifunctional yeast alpha 6 beta 6 fatty acid synthase and that these centers operate independently.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduced virulence of Yersinia enterocolitica by copper-induced injury.

A sublethal concentration of copper (0.75 mg/liter) caused substantial injury (87 to 95%) of Yersinia enterocolitica serotype O:8 cells in 72 h at 4 degrees C without producing extensive cell death. Copper-injured cells had a higher 50% lethal dose in mice (2,700 CFU) than uninjured cells (150 CFU). This reduced virulence correlated with more rapid clearance of the injured cells from the blood of mice after intravenous inoculation. A possible role of the liver in this process was shown by significant cell accumulation in mouse livers when copper-injured Y. enterocolitica cells were administered, compared with uninjured bacteria. In vitro studies with isolated mouse liver membranes showed higher titers of aggregation with copper-injured cells than control cells. The in vitro aggregation reaction and blood clearance activity in vivo were abolished by sugars that are known to interact with a hepatic lectin. Our data suggest that copper-induced injury reduces the virulence of Y. enterocolitica and that the liver may be involved in nonimmune rapid clearance of the injured cells, probably by interaction with a hepatic lectin(s).     

Phosphorylation of rat liver glucocorticoid receptor

Rat liver glucocorticoid-receptor complex (GRc) was purified 2000-fold by a combination of methods including (NH4)2SO4-fractionation and phosphocellulose and DNA-cellulose chromatography. The purified glucocorticoid receptor preparation contained a major peptide of Mr = 90,000 and the GRc sedimented as 4 S in 5-20% sucrose gradients. An additional peptide of Mr = 45,000 (45K) was also observed. Some preparations yielded only the Mr = 90,000 (90K) peptide suggesting that the 45K peptide may be a proteolyzed portion of the 90K protein. The purified GRc was incubated with [gamma-32P]ATP in the presence of cAMP-dependent kinase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the above preparation revealed the presence of two 32P-containing bands with apparent Mr = 90,000 and 45,000. The 32P incorporation was dependent on the availability of divalent cation (Mg2+). GRc in cytosol labeled with [3H]dexamethasone mesylate and purified as above co-migrated with 32P-containing bands. GRc was also purified from cytosol obtained from livers of rats injected with [32P]orthophosphate. Both 32P and 3H bands were associated with 90K and 45K peptides. Our results indicate that rat liver glucocorticoid receptor is a phosphoprotein and that both the phosphorylated peptides 90K and 45K also contain the steroid and the DNA binding regions of the glucocorticoid receptor.     

Nitrate metabolism in the cyanobacterium Anabaena cycadeae: Regulation of nitrate uptake and reductase by ammonia

Nitrogen regulation of nitrate uptake and nitrate reductase (EC 1.7.99.4) was studied in the cyanobacterium Anabaena cycadeae Reinke and its glutamine auxotroph. Development of the nitrate uptake system preceded, and was independent of, the development of the nitrate reductase system. The levels of both systems were several-fold higher in the glutamine auxotroph lacking glutamine synthetase (EC 6.3.1.2) than in the wild type strain having normal glutamine synthetase activity. The nitrate uptake system was found to be NH4-repressible and the nitrate reductase system NO₃⁻-inducible. NH₄⁺ was the initial repressor signal for the uptake process which was involved in the control of the NO₃⁻inducible reductase system.     

Root turnover and production by14C dilution: implications of carbon partitioning in plants

Summary Estimates of belowground net primary production (BNP) obtained by using traditional soil core harvest data are subject to a variety of potentially serious errors. In a controlled growth chamber experiment, we examined the aboveground-belowground, labile to structural tissue, and plant to soil dynamics of carbon to formulate a¹⁴C dilution technique for potential successful application in the field and to quantify sources of error in production estimates.Despite the fact that the majority of net¹⁴C movement between above- and belowground plant parts occurred between the initial labeling and day 5, significant quantities of¹⁴C were incorporated into cell-wall tissue throughout the growing period. The rate of this increase at late sampling dates was greater for roots than for shoots. Total loss of assimilated¹⁴C was 47% in wheat and 28% in blue grama. Exudation and sloughing in wheat and blue grama, respectively, was 15 and 6% of total uptake and 22 and 8% of total plant production.When root production estimates by¹⁴C dilution were corrected for the quantities of labile¹⁴C incorporated into structural carbon between two sampling dates, good agreement with actual production was found. The error associated with these estimates was ±2% compared with a range of –119 to –57% for the uncorrected estimates. Our results suggest that this technique has potential field application if sampling is performed the year after labelling.Sources of errors in harvest versus¹⁴C dilution estimates of BNP are discussed.     

Glucagon-stimulated phosphorylation of rat liver glycogen synthase in isolated hepatocytes

Addition of glucagon (20 nM) to the isolated hepatocytes from 24-h starved male rats results in an inactivation of glycogen synthase. The A0.5 for glucose-6-P is increased 2-fold over the control but the S0.5 for UDP-glucose is not significantly affected. The glucagon-stimulated inactivation of glycogen synthase is also accompanied by a 60-120% increase in the phosphorylation of the synthase. Glycogen synthase labeled with 32P by incubation of the hepatocytes with [32P] PO4(3-) was recovered by immunoprecipitation and the resulting immunoprecipitate was subjected to tryptic digestion. Analysis of the 32P-labeled peptides reveals that the sites corresponding to those phosphorylated by cAMP-dependent protein kinase and glycogen synthase (casein) kinase-1 (Itarte, E., and Huang, K.-P. (1979) J. Biol. Chem. 254, 4052-4057) are rapidly phosphorylated in response to glucagon. These results demonstrate that glucagon not only triggers the activation of cAMP-dependent protein kinase through an increase in the intracellular level of cAMP but also, by an unknown mechanism, activates a Ca2+- and cAMP-independent protein kinase.