Interrod forces in aqueous gels of tobacco mosaic virus.

The lateral separation of virus rod particles of tobacco mosaic virus has been studied as a function of externally applied osmotic pressure using an osmotic stress technique. The results have been used to test the assumption that lattice equilibrium in such gels results from a balance between repulsive (electrostatic) and attractive (van der Waals and osmotic) forces. Results have been obtained at different ionic strengths (0.001 to 1.0 M) and pH's (5.0 to 7.2) and compared with calculated curves for electrostatic nad van der Waals pressure. Under all conditions studied, interrod spacing decreased with increasing applied pressure, the spacings being smaller at higher ionic strengths. Only small differences were seen when the pH was changed. At ionic strengths near 0.1 M, agreement between theory and experiment is good, but the theory appears to underestimate electrostatic forces at high ionic strengths and to underestimate attractive forces at large interrod spacings (low ionic strengths). It is concluded that an electrostatic-van der Waals force balance can explain stability in tobacco mosaic virus gels near physiological conditions and can provide a good first approximation elsewhere.     

Modulation of Epstein-Barr virus-induced B-cell activation by concanavalin A

Direct addition of the T-cell mitogen, concanavalin A (Con A), to cultures of Epstein-Barr virus (EBV)-stimulated peripheral blood mononuclear cells (PBMC) resulted in a dose-dependent inhibition of immunoglobulin M (IgM) secreted in the supernatant, as measured by an enzyme-linked immunosorbent assay. Furthermore, Con A inhibited IgM secretion of isolated T-depleted cells stimulated with EBV, and both the proliferation and IgM secretion of EBV-driven lymphoblastoid cell lines. T-Enriched cells, precultured for 48 hr with Con A, were also able to suppress the IgM response of fresh autologous PBMC stimulated with EBV. This suppression was radiation sensitive (2000 rad), a procedure which resulted in enhancement of the IgM secretion of the responder cells in two out of three experiments. Studies on the long-term effects of Con A showed that the early suppression of IgM secretion was transient and that the mitogen prevented the development of the cytotoxic T-cell response normally seen with lymphocytes from EBV-seropositive donors after 5 weeks of culture. Thus, Con A appears to modulate human lymphocyte responses to EBV by multiple mechanisms.     

"Silent" sites in Drosophila genes are not neutral: evidence of selection among synonymous codons

The patterns of synonymous codon usage in 91 Drosophila melanogaster genes have been examined. Codon usage varies strikingly among genes. This variation is associated with differences in G+C content at silent sites, but (unlike the situation in mammalian genes) these differences are not correlated with variation in intron base composition and so are not easily explicable in terms of mutational biases. Instead, those genes with high G+C content at silent sites, resulting from a strong "preference" for a particular subset of the codons that are mostly C- ending, appear to be the more highly expressed genes. This suggests that G+C content is reduced in sequences where selective constraints are weaker, as indeed seen in a pseudogene. These and other data discussed are consistent with the effects of translational selection among synonymous codons, as seen in unicellular organisms. The existence of selective constraints on silent substitutions, which may vary in strength among genes, has implications for the use of silent molecular clocks.      

Calcium signals recorded from cut frog twitch fibers containing tetramethylmurexide

The Ca indicator tetramethylmurexide was introduced into cut fibers, mounted in a double-Vaseline-gap chamber, by diffusion from the end-pool solutions. The indicator diffused rapidly to the central region of a fiber where optical recording was done and, if removed, diffused away equally fast. The time course of concentration suggests that, on average, a fraction 0.27 of indicator was reversibly bound to myoplasmic constituents and the free diffusion constant was 1.75 x 10(-6) cm2/s at 18 degrees C. The shape of the resting absorbance spectrum suggests that a fraction 0.11-0.15 of tetramethylmurexide inside a fiber was complexed with Ca. After action potential stimulation, there was a rapid transient change in indicator absorbance followed by a maintained change of opposite sign. The wavelength dependence of both changes matched a cuvette Ca-difference spectrum. The amplitude of the early peak varied linearly with indicator concentration and corresponded to an average rise in free [Ca] of 17 microM. These rather diverse findings can be explained if the sarcoplasmic reticulum membranes are permeable to Ca-free indicator. Both Ca-free and Ca-complexed indicator inside the sarcoplasmic reticulum would appear to be bound by diffusion analysis and the Ca-complexed form would be detected by the resting absorbance spectrum. The transient change in indicator absorbance would be produced by myoplasmic Ca reacting with indicator molecules that freely diffuse in myoplasmic solution. The maintained signal, which reports Ca dissociating from indicator complexed at rest, would come from changes within the sarcoplasmic reticulum. A method, based on these ideas, is described for separating the two components of the tetramethylmurexide signal. The estimated myoplasmic free [Ca] transient has an average peak value of 26 microM at 18 degrees C. Its time course is similar to, but possibly faster than, that recorded with antipyrylazo III (Maylie, J., M. Irving, N. L. Sizto, and W. K. Chandler. 1987. Journal of General Physiology. 89:83-143).     

Studies of nucleotides of growth-plate cartilage: evidence linking changes in cellular metabolism with cartilage calcification

The objective of this study was to examine the nucleotides of chick growth-plate cartilage and to measure the concentration of adenine nucleotides in the pre-mineralizing and mineralizing zones. Nucleotides were isolated from the two regions using a rapid-freezing technique and the concentration of individual components was ascertained by HPLC. The actual values of ATP, ADP, and other nucleotides in cartilage was low. The lowest values were recorded in the mineralized zone. In this latter zone the energy charge ratio and the ATP/ADP ratio were depressed. This was probably due to 0₂-related inhibition of mitochondrial oxidative activity . Additionally, the percentage of octanoate, a short-chain fatty acid that accumulates when aerobic metabolism is disturbed, was found to have increased in the calcifying zone. These findings suggest that calcification of cartilage is associated with hypoxia-related modulation of chondrocyte metabolism.     

A method for measuring the content of a specific messenger ribonucleic acid in Escherichia coli

A method is described for measuring the porportion of a specific messenger RNA in the total RNA extracted from pulse-labelled cells. A model system consisting of total ribosomal RNA and Escherichia coli DNA is used to validate the method and to define the conditions under which it can be used.     

Erythritol as a Selective Substrate for the Growth of Serratia marcescens

Serratia marcescens grew on a basal medium containing 0.5% erythritol as sole source of carbon for growth and energy. Only an occasional strain of Enterobacter aerogenes among several members of the family Enterobacteriaceae were able to utilize erythritol.     

Clonal Variation in Paramecium II. a Comparison of Stable and Unstable Clones of the Same Serotype

Paramecium generally expresses only one antigen on its surface from among an array of antigens. This mutual exclusion of antigens now has been shown in certain instances to be illusory. Unstable clones which will give rise to subclones with new serotypes possess several antigens. Unstable clones, even though they manifest only one serotype, continually manufacture an antigen other than the surface antigen characteristic of the serotype.     

Comparison of Deoxyribonucleic Acid Uptake and Marker Integration in Bacilli and Protoplasts of Bacillus subtilis

trp(+)his(-) donor deoxyribonucleic acid (DNA) was added to highly competent trp(-)his(+) recipient bacilli and to protoplasts prepared from these bacilli, and the cell-DNA complexes were incubated for 30 min. The complexes were then washed and lysed, and their DNA was analyzed on a trp(-)his(-) strain for the donor marker trp(+), the resident marker his(+), and for the recombinant trp(+)his(+) combination. The extracts of the bacillary complexes contained a normal percentage of donor markers (0.1-0.2%), and the number of trp(+)his(+) doubles (20% of all trp(+) transformants) indicated that the donor DNA had become integrated into the resident genomes. The protoplast complexes contained 10 to 1,000 times fewer donor markers and almost no recombinants. This indicated that, in protoplasts, marker uptake was minimal and recombination was absent. Uptake was also measured with (3)H-labeled DNA. On the average, protoplasts took up one-fiftieth as much DNA as bacilli. It was concluded that, probably, protoplasts took up no DNA at all, that there were no DNA affinity sites on the surface of the protoplasts, and that the residual marker and radioactivity uptake was due to imperfections in the experimental system. The data and conclusions differed sharply from earlier ones of Hirokawa and Ikeda despite the fact that the techniques of these authors were followed in repeat experiments.     

Clinical Aspects of Thyroid Cancer

Confusion still prevails regarding the selection of patients with thyroid nodules for surgical treatment. Classical features of malignancy do not apply to growths of the thyroid gland. Duration, size, presence of calcification, scintiscanning and response to thyroid feeding are not, in themselves, reliable indicators of the absence or presence of malignancy. In 78 personal thyroidectomies there was a 60% overall neoplasm rate and a 25% malignancy rate. Operation is indicated for the thyroid lesion which is solitary, cold, unresponsive to thyroid feeding or accompanied by obvious evidence of malignancy. Recent experience indicates that thyroid surgery has a low morbidity and negligible mortality. Surgical treatment of the common forms of thyroid cancer yields excellent results if it is complete and is expertly done.