The dynamical structure of the RNA in alfalfa mosaic virus studied by 31P-nuclear magnetic resonance

The structure of the viral RNA in alfalfa mosaic virus (AlMV) was investigated by means of 31P-nuclear magnetic resonance (NMR). It was found that the 31P-NMR line width of AlMV Top a particles is significantly smaller than that of the larger Bottom particles. At low temperatures, the totational correlation time of the 31P nuclei essentially equals the tumbling rate of the virus particle, indicating that the RNA is contained rigidly inside the virion. At more elevated temperatures, the NMR line width sharpens more than expected on the basis of viscosity changes and the RNA exhibits internal mobility. The occurrence of internal mobility is paralleled by an increased internal mobility of the N-terminal part of the coat protein, as could be observed by 1H-NMR spectroscopy. The influence of EDTA on the 31P-NMR line width appeared to be negligible, which is in agreement with the idea that AlMV does not 'swell' like several other RNA-containing plant viruses.     

Measurements of cytoplasmic and vacuolar pH in Neurospora using nitrogen-15 nuclear magnetic resonance spectroscopy

The nitrogen-15 chemical shift of the N1 (tau)-nitrogen of 15N-labeled histidine and the half-height line widths of proton-coupled resonances of the delta- and omega,omega'-nitrogens of 15N-labeled arginine and of the alpha-nitrogens of 15N-labeled alanine and proline were measured in intact mycelia of Neurospora crassa to obtain to estimates of intracellular pH. For intracellular 15N-labeled histidine, the N1 (tau)-nitrogen chemical shift was 200.2 ppm. In vitro measurements showed that the chemical shift was slightly affected by the presence of phosphate, with which the basic amino acids may be associated in vivo. These considerations indicate a pH of 5.7-6.0 for the environment of intracellular histidine. The half-height line widths of the delta- and omega,omega'-nitrogens of [15N]arginine were 15 and 26 Hz, respectively. In vitro studies showed that these line widths also are influenced by the presence of phosphate, and, after suitable allowance for this, the line widths indicate pH 6.1-6.5 for intracellular arginine. The half-height line widths for intracellular alanine and proline were 17 and 12 Hz, respectively, which are consistent with an intracellular pH of 7.1-7.2. Pools of histidine and arginine are found principally in the vacuole of Neurospora, most likely in association with polyphosphates. Proline and alanine are cytoplasmic. The results reported here are consistent with these localizations and indicate that the vacuolar pH is 6.1 +/- 0.4 while the cytoplasmic pH is 7.15 +/- 0.10. Comparisons of these estimates with those obtained by other techniques and their implications for vacuolar function are discussed.     

Nuclear magnetic resonance studies of cis-syn, trans-syn, and 6-4 photodimers of thymidylyl(3'-5')thymidine monophosphate and cis-syn photodimers of thymidylyl(3'-5')thymidine cyanoethyl phosphotriester

Three out of four possible photodimers of thymidylyl(3'-5')thymidine monophosphates (i.e., cis-syn, 6-4, and one of the trans-syn) and two structural isomers (i.e., R and S forms) of cis-syn-thymidylyl(3'-5')thymidine cyanoethyl phosphotriester have been isolated and purified from the reaction mixtures after UV irradiation and studied by multinuclear magnetic resonance Spectroscopy. All five inter thymine base linked photodimers have grossly similar structures which are quite different from those of the parent thymidylyl(3'-5')thymidine. The base of Tp- is in the syn conformation, and that of -pT it is in the anti conformation. The sugar puckering of Tp- is dominated by the 2E conformer, but in -pT it is in 4E; except for the conformer around C5'-O5' bond, the 6-4 isomer is very similar to those of cis-syn and trans-syn conformation. As expected, there are sugar-phosphate backbone distortions in the phosphotriesters, due to the neutralization of the negative charge of the phosphate. In general the structures of all five photodimers are very close to those of the cis-syn photodimer of thymidylyl(3'-5')thymidine monophosphate cyanoethyl ester as studied by X-ray diffraction [Cadet, J., Voituriez, L., Hruska, F. E., & Grand, A. (1985) Biopolymers 24, 897-903; Hruska, F. E., Voituriez, L., Grand, A., & Cadet, J. (1986) Biopolymers 25, 1401-1417]. While the trans-syn photodimer has two structural isomers, only one [C6(of Tp-)-R] was produced by the UV irradiation and studied.     

Modulation induction of the T3 antigen by OKT3 antibody is monocyte dependent

We investigated the influence of monocytes on the susceptibility of the T3 antigen on human T cells to modulation induction by OKT3 antibody. In the absence of monocytes, the T3 antigen was only minimally susceptible to modulation. After the addition of 20% monocytes to the culture, however, complete modulation was readily observed. Furthermore, we found that even in the absence of OKT3 antibody, monocytes were able to down-regulate the expression of the T3 antigen, although to a lesser extent. The ability of monocytes to enhance antigenic modulation proved to be a more general phenomenon. Each individual T cell antigen, however, differed in its susceptibility to modulation by antibody, monocytes, or both, thereby establishing its own characteristic pattern. In addition, after complete modulation of the T3 antigen, the addition of monocytes to the culture thereafter had a distinct inhibitory effect on the reexpression of the T3 antigen. Monocyte enhancement of T3 modulation is significantly reduced when using the OKT3 F(ab')2 fragment, as is OKT3 mitogenesis. After pulsing the monocytes with OKT3 antibody before adding them to the culture, T3 modulation became nearly complete even in the absence of added OKT3 antibody. Monocyte-induced modulation proved not to be MHC restricted, thus allowing for comparative analysis of this effect between monocytes and other cell types. A moderate, however, incomplete modulation enhancement was observed with the human monocyte cell line U937 and with Daudi cells. This finding proved to coincide with the distinct ability of these cell lines to bind OKT3 antibody by their Fc receptors, as was the case with monocytes. In contrast, neither Fc receptor binding nor T3 modulation enhancement was observed with the cell lines Cess and G7. In addition, no effective T3 modulation was observed with glutaraldehyde-fixed monocytes. The overall results seem to indicate that effective modulation of the T3 antigen by OKT3 antibody requires the active participation of Fc receptors on monocytes.     

Direct analysis of growth factor requirements for isolated human fetal hepatocytes

Summary Hepatocytes were isolated from human fetal liver in order to analyze the direct effects of growth factors and hormones on human hepatocyte proliferation and function. Mechanical fragmentation and then dissociation of fetal liver tissue with a collagenase/dispase mixture resulted in high yield and viability of hepatocytes. Hepatocytes were selected in arginine-free, ornithine-supplemented medium and defined by morphology, albumin production and ornithine uptake into cellular protein. A screen of over twenty growth factors, hormones, mitogenic agents and crude organ and cell extracts for effect on the stimulation of hepatocyte growth revealed that EGF, insulin, dexamethasone, and factors concentrated in bovine neural extract and hepatoma cell-conditioned medium supported attachment, maintenance and growth of hepatocytes on a collagen-coated substratum. The population of cells selected and defined as differentiated hepatocytes had a proliferative potential of about 4 cumulative population doublings. EGF and insulin synergistically stimulated DNA synthesis in the absence of other hormones and growth factors. Although neural extracts enhanced hepatocyte number, no effect on DNA synthesis of neural extracts or purified heparin-binding growth factors from neural extracts could be demonstrated in the absence or presence of defined hormones, hepatoma-conditioned medium or serum. Hepatoma cell-conditioned medium had the largest impact on both hepatocyte cell number and DNA synthesis under all conditions. Dialyzed serum protein (1 mg/ml) at 10 times higher protein concentration had a similar effect to hepatoma cell-conditioned medium (100 μg/ml). The results suggest that hepatoma cell conditioned medium may be a concentrated and less complicated source than serum for purification and characterization of additional normal hepatocyte growth factors. This work was supported by NIH grant DK35310. Editor’s statement Many investigators have struggled with the special problems associated with culture of differentiated hepatocytes. In this paper attention is given to the specific growth factor requirements for fetal human hepatocytes. The observation that factors from hepatoma conditioned medium or neural extracts enhanced the growth of the cells may indicate that additional growth factors are to be identified that are important in the survival and proliferation of hepatocytes, and may also indicate that the malignant transformation of these cells may involve the production of autocrine growth stimulators.     

Nuclear magnetic resonance study on the exchange behavior of the NH-N protons of a ribonucleic acid miniduplex

The exchange behavior of the guanine N(1) and uracil N(3) protons in the self-complementary hexanucleotide r(ApApGpCpUpU) has been studied at 5 degrees C in 80% H2O/20% D2O by proton NMR. Under these conditions, the hexanucleotide forms a stable miniduplex. The exchange rate of all Watson-Crick NH protons is unaffected by addition of trifluoroethylamine up to 0.07 M. On the other hand, addition of phosphate buffer, pH 6.9, enhances the exchange rate of the uracil N(3) protons of both terminal and internal A X U base pairs but does not influence the exchange rate of the guanine N(1) protons of the central G X C base pairs. Catalysis by increased phosphate concentrations results in an open-limited rate of the internal A X U base pairs with kex = 233 s-1, equivalent to a lifetime of 4.3 ms. The proton exchange of the central G X C is regulated by the opening rate of the central core of the miniduplex. On the other hand, the sensitivity of the exchange rate of internal as well as of terminal A X U base pairs can be explained by their reduced lifetime due to end "fraying" and a subsequent catalysis of the exchange process from the opened state. These results suggest that it may be possible to probe labilized parts of RNAs such as tRNA by gradual addition of the exchange catalyst phosphate and to monitor their exchange rates by proton NMR.     

Protein synthesis and secretion in the human epididymis and immunoreactivity with sperm antibodies

The synthesis and secretion of proteins in the different regions of the human epididymis were studied in vitro. Epididymal tissues obtained from patients undergoing castration for prostatic carcinoma or from cadavers were incubated in the presence of [35S]methionine, and the resulting radiolabeled proteins were analysed on SDS-PAGE. The corpus region was found to be the most active segment in total protein synthesis. Significant qualitative and quantitative changes were observed in the pattern of proteins secreted from the different epididymal regions. To establish those epididymal proteins that interact with maturing sperm, the secreted products were immunoreacted with antibodies raised against a Triton X-100 extract of ejaculated human sperm heads. The antibodies react mainly with the head region of ejaculated spermatozoa as judged by indirect immunofluorescence. Protein A-gold labeling of freeze-fracture images showed gold particle distribution on the sperm plasma membrane. Western blot analysis of the secreted proteins revealed four bands (66, 37, 32, and 29 kDa) in the proximal regions and six additional bands (80, 76, 48, 27, 22, and 17 kDa) in the distal part of the epididymis. Immunoprecipitation of the secreted proteins with these antibodies revealed six radioactive bands of 170, 80, 76, 60, 48, and 37 kDa, which indicates that certain proteins of epididymal origin bind to the sperm plasma membrane.     

Studies of Sarcocystis in Malaysia. II. Comparative ultrastructure of the cyst wall and zoites of Sarcocystis levinei and Sarcocystis fusiformis from the water buffalo, Bubalus bubalis.

The two species of Sarcocystis--S. levinei and S. fusiformis from the water buffalo, Bubalus bubalis, show some ultrastructural similarities in their cyst wall and zoites. The zoites of both species are of about the same size, banana-shaped and have 22 subpellicular microtubules, numerous micronemes, eight rhoptries, a micropore in the region of the micronemes, an elongated mitochondrion, and a nucleus. S. levinei has 200--300 micronemes and S. fusiformis has about 400. The sarcocysts of both species are trabeculated and their cyst walls have cytophaneres containing annulated fibrils and coarse, electron dense granules. The cytophaneres of S. levinei are sloping, with irregular, wavy outlines, whereas S. fusiformis has the cauliflower-type of cytophaneres. This difference in the appearance of the cytophaneres, together with the difference in size of the sarcocysts and their definitive hosts, further confirms that S. levinei and S. fusiformis are two distinct species in the water buffalo.