Unit Cell Hypothesis for Streptococcus faecalis

The mass doubling times of exponential-phase cultures of Streptococcus faecalis were varied from 30 to 110 min by omitting glutamine from a defined growth medium and providing different concentrations of glutamate (ranging from 300 to 14 μg/ml). After Formalin fixation, cells were dried by the critical point method, and carbon-platinum replicas were prepared. The surface area and volume of cell poles seen in these replicas were estimated by a computer-assisted, three-dimensional reconstruction technique. It was found that the amount of surface area and volume of poles seen in these replicas were independent of the growth rate of culture from which the samples were taken. These observations were consistent with the unit cell model hypothesis of Donachie and Begg, in which a small number of surface sites would produce a constant amount of new cell surface regardless of the mass doubling time of the culture. However, measurements of the thickness of the cell wall taken from thin sections of the same cells showed that the cell wall increased in thickness as a function of the increase in cellular peptidoglycan content which occurs when the growth rate of this organism is slowed down by a decrease in glutamate concentration. Thus, it would seem that although the size of polar shells made by S. faecalis is invariant with growth rate, the amount of wall precursors used to construct these shells is not.     

Effects of food availability on the valve movements and feeding behavior of juvenile Crassostrea Virginica (Gmelin). I. Valve movements and periodic activity

The effects of changes in the availability of algal food on the valve movements of juvenile Crassostrea virginica (Gmelin) were investigated. Individual oysters were subjected to different conditions: (1) unfed in filtered sea water; (2) continuously fed, in which oysters were given an algal suspension maintained at a constant level (50 000 cells/ml) by an automatic turbidostat; (3) discontinuously fed, where oysters were alternately fed with the turbidostat for 12 h and unfed for 12 h; and (4) batch fed, in which oysters were given specific daily rations at two ration levels (maximum and 40%). Valve movements were concurrently recorded and periods of activity (valves open) and quiescence (valves closed) measured.Oysters fed continuously remained open an average of 94.3% of the time, whereas unfed oysters were open 35.1% of the time. Discontinuously fed animals were open 95.7% of the time during the times of feeding, but 60.6% of the time during the unfed periods. Activity in the batch-fed oysters was related to the ambient algal concentration in that both the percentage time open/hour and the duration of valve openness decreased with decreasing concentration. Time series analysis of valve movements showed that oysters exhibited a 24-h periodicity of activity when subjected to a 24-h feeding schedule (discontinuous and batch groups) but exhibited no consistent periodicity under the continuous feeding or unfed conditions.     

Demonstration of an internal fraction plane in cell walls of Streptococcus faecalis and Streptococcus mutans.

The proposed lower internal density of the gram-positive wall was confirmed by observed an internal fracture plane in the walls of Streptococcus faecalis and Streptococcus mutans. However, the granular surfaces produced by this cleavage appeared to be more of a reflection of distortion during preparation than of subunit construction.     

Reversible inhibition of mitochondrial respiratory control by tetrabutylammonium bromide.

Influences of tetrabutylammonium bromide as a phosphorylation inhibitor and as an uncoupler of oxidative phosphorylation in rat liver mitochondria were reversed by washing the organelles. Uncoupling by 2,4-dinitrophenol was also reversible whereas gramicidin and the detergents, sodium dodecylsulfate and cetyltrimethylammonium bromide, were tightly bound uncouplers and they were not substantially removed by simple washing.     

DNA sequence organization in the genomes of five marine invertebrates

The arrangement of repetitive and non-repetitive sequence was studied in the genomic DNA of the oyster (Crassostrea virginica), the surf clam (Spisula solidissima), the horseshoe crab (Limulus polyphemus), a nemertean worm (Cerebratulus lacteus) and a jelly-fish (Aurelia aurita). Except for the jellyfish these animals belong to the protostomial branch of animal evolution, for which little information regarding DNA sequence organization has previously been available. The reassociation kinetics of short (250-300 nucleotide) and long (2,000-3,000 nucleotide) DNA fragments was studied by the hydroxyapatite method. It was shown that in each case a major fraction of the DNA consists of single copy sequences less than about 3,000 nucleotides in length, interspersed with short repetitive sequences. The lengths of the repetitive sequences were estimated by optical hyperchromicity and S1 nuclease measurements made on renaturation products. All the genomes studied include a prominent fraction of interspersed repetitive sequences about 300 nucleotides in length, as well as longer repetitive sequence regions.     

Binding of glucocorticoid receptors to DNA.

DNA has been implicated as the nuclear acceptor for receptor-glucocorticoid complexes. The present study concerns the interaction of these complexes, isolated from cultured rat hepatoma cells, with purified DNA. This association is rapid, reaching a maximum within a few minutes at 0 degrees, whereas dissociation requires several hours. DNA binds neither free glucocorticoids nor those complexed with transcortin or cytosol proteins different from the receptor. Receptors which are not complexed by steroid have little or no affinity for DNA. "Activation," necessary for the binding of receptor-steroid complexes to isolated nuclei, also enhances DNA binding. The capacity of DNA for binding receptor-steroid complexes is large; saturation was not observed at the complex concentrations studied, using either crude or partially purified receptor preparations. The association of complexes with DNA is inhibited by divalent cations, at increasing ionic strengths, and by mercurial reagents. Complexes bind equally well to bacterial, bacteriophage, or rat DNA; however, there was either no or substantially reduced binding by bacterial 23 S rRNA. The binding of complexes to native DNA is roughly 3-fold greater than to denatured DNA. These characteristics are consistent with the possibility that DNA is the nuclear acceptor for receptor-glucocorticoid complexes; however, the actual composition of the acceptor sites remains unknown.     

Organization of mesosomes in fixed and unfixed cells.

After the addition of glutaraldehyde (GA) to cells incubated at 3 or 37 degrees C, mesosomes were observed with increasing frequencies in freeze fractures of cells. These increases were related to the kinetics with which GA cross-linked adjacent amino acids. Upon the addition of GA, mesosomes were first observed in the periphery of freeze-fractured cells usually attached to septal membranes. However, the time, while the septal attachment sites were maintained, the "bodies" of the mesosomes were observed to move toward the center of the cytoplasm. This centralization process was much more rapid at 37 than at 3 degrees C. It is hypothesized that upon fixation, or receipt of some physical insult, mesosome precursors found in undisturbed cells undergo a change in state that results in their visibility in freeze fractures.     

Nuclear components responsible for the retention of steroid--receptor complexes, especially from the standpoint of the specifcity of hormonal responses.

1. By covalently linking nuclear components from hormone-sensitive cells to Sepharose 2B, it is possible to investigate the interaction between nuclear components and cytoplasmic receptor-steroid complexes by affinity chromatography. 2. Many factors are implicated in the specifity of nuclear-cytoplasmic interactions, including the nature of the nuclear components, the presence of the cytoplasmic receptor protein and the provision of the appropriate steroid ligand. 3. Two distinct sets of binding sites are present in nuclear extracts immobilized to Sepharose 2B, namely a small number of specific high-affinity sites and a larger number of non-specific low affinity-sites. 4. Considerable evidence supports the importance of the high-affinity binding sites in the manifestation of hormonal specificity in different tissues. Although the study has centred largely on androgenresponsive systems, the findings are germane to cytoplasmic-nuclear interactions in general. 5. The high-affinity or acceptor sites in nuclear extracts reside in the basic but non-histone protein fraction. 6. Hormonal specificity is seemingly maintained by both the cytoplasmic and nuclear components, and the results are discussed in the context of the mechanism of action of steroid hormones.