Bacteriophage T4 Head Maturation: Release of Progeny DNA from the Host Cell Membrane

We have presented a new approach to studying bacteriophage T4 head maturation. Using a modified M-band technique, we have shown that progeny deoxyribonucleic acid (DNA) was synthesized on the host cell membrane throughout infection. This DNA was released from the membrane later in infection as the result of formation of the phage head; detachment of the DNA required the action of gene products 20, 21, 22, 23, 24, 31, 16, 17 and 49, known to be necessary for normal head formation. Gene products 2, 4, 50, 64, 65, 13 and 14, also involved in head morphogenesis were not required to detach progeny DNA from the membrane; the presence of the phage tail and tail fibers also was not required. DNA was released in the form of immature heads and initially was sensitive to deoxyribonuclease (DNase). Conversion to DNase resistance followed rapidly. The amount of phage precursors present at the time of DNA synthesis determined the time of onset and detachment rate of DNA from the M band as well as the kinetics by which the detached DNA become DNase resistant.     

Transport and metabolism of galactose in rat kidney cortex

1. Analysis of transport of d-galactose was complicated by metabolism of the compound but appeared to have two components: a substrate-saturable component and a diffusion component. At low substrate concentration (<1mm) active transport was observed. Accumulation of galactose was largely independent of Na(+) concentration. The apparent K(m) for this component was 0.2mm. At substrate concentrations above 1mm the active transport system appeared saturated and further increases in substrate concentration resulted in a linear increase in the rate of galactose accumulation, but no concentration gradient was formed. 2. d-[1-(14)C]Galactose (2mm) was metabolized to (14)CO(2) by rat kidney-cortex slices incubated at 37 degrees C, at the rate of 68nmol/h per 100mg of tissue. 3. Intracellular components from such incubations were separated into a neutral fraction, the only major labelled component being galactose, and a phosphorylated fraction. 4. Phosphorylated metabolites found in galactose-incubated slices increased with increasing substrate concentration and achieved a limiting value of 0.42mm after 60min of incubation. 5. Galactose uptake was inhibited by anaerobiosis, dinitrophenol and phlorrhizin. 6. Methyl alpha-d-glucoside and d-glucose partially inhibited galactose uptake only at ratios of 100:1. 7. The presence of pyruvate did not decrease galactose metabolism although it did decrease production of (14)CO(2) from [1-(14)C]galactose. Gluconeogenesis occurred in the presence of pyruvate and (14)C from galactose was found in glucose. 8. Rat kidney-cortex slices metabolized 2mm-[1-(14)C]galactonate to (14)CO(2) at a rate of 20nmol/h per 100mg of tissue.     

The response by microorganisms to steady-state growth in controlled concentrations of oxygen and glucose. II. Saccharomyces carlsbergensis

The growth of Saccharomyces carlsbergensis in continuous culture has been studied when dissolved oxygen and glucose concentrations were held constant at a series of steady-state levels. Both oxygen and glucose controlled the degree of aerobic metabolism and of ethanolic fermentation. When the glucose uptake rate was low (between 1.2 and 2.8 mmoles per hour per gram of yeast) the relative distribution of glucose between ethanolic and aerobic fermentation was sensitive to oxygen: when dissolved oxygen was near to saturation, glucose metabolism was 0.98 aerobic; when dissolved oxygen was 0.01 saturated, 0.8 of intake glucose metabolism was by ethanolic fermentation. On the other hand when glucose intake was high (between 7.6 and 18.2 mmoles) metabolism was predominately by ethanolic fermentation even when dissolved oxygen concentration was at saturation. The extent, to which catabolism proceeded by an anaerobic or aerobic pathway, as judged by ethanol production, was controlled more by the uptake of glucose than of oxygen.     

The active centre of triose phosphate isomerase

1. Cystamine (2,2'-diaminodiethyl disulphide) caused an unmasking of mitochondrial adenosine triphosphatase and a leakage of Mg(2+) from the mitochondria, and decreased the stimulation of adenosine triphosphatase by 2,4-dinitrophenol. When Mg(2+) was added, cystamine potentiated the activation of adenosine triphosphatase by 2,4-dinitrophenol. 2. Cystamine was without effect on the adenosine triphosphatase of disrupted mitochondria. 3. Cystamine was moderately potent as an uncoupling agent and as an inhibitor of the [(32)P]P(i)-ATP exchange reaction. 4. Cysteamine (2-aminoethanethiol) was without the above effects, when special precautions were taken to counteract its autoxidation. 5. The effects of cystamine should probably be ascribed to its disulphide group, since the diamine cadaverine protected slightly against the loss of Mg(2+) and the decrease of 2,4-dinitrophenol-stimulated adenosine-triphosphatase activity caused by aging of the mitochondria. It is suggested that cystamine acts by a breakdown of mitochondrial permeability barriers.     

Breeding Systems of Three Tree Ferns: Alsophila firma (Cyatheaceae), Cyathea stipularis (Cyatheaceae), and Lophosoria quadripinnata (Lophosoriaceae)

Abstract Breeding-system data have been available for a large number and diverse array of angio-sperms for a relatively long time. In contrast, breeding systems of ferns and their allies (pteridophytes) have only recently been examined, and breeding-system data from natural populations of sporophytes are still lacking for pteridophytes representing many life-history strategies. Few studies, for example, have examined breeding systems of tropical pteridophytes, and no breeding-system data are available for tree ferns. We therefore examined the breeding systems of three species of tree ferns from Costa Rica, Alsophila firma (Cyatheaceae), Cyathea stipularis (Cyatheaceae), and Lophosoria quadripinnata (Lophosoriaceae) using enzyme electro-phoresis. Genetic data were used to estimate intragametophytic self-fertilization and F , the fixation index. Analysis of genetic data indicates that the gametophytes of these three species predominantly cross-fertilize; all three species would be characterized as outcrossers. However, some population-to-population variation in breeding system was detected in all three species. Outcrossing also typifies a diverse array of temperate ferns. Thus, despite the potential for self-fertilization, outcrossing appears to characterize the majority of pteridophytes representing a variety of evolutionary lineages, life-history strategies, and environments.     

Annual nitrous oxide flux and soil nitrogen characteristics in sagebrush steppe ecosystems

Soil nitrogen transformations and nitrous oxide fluxes were measured in a range of sagebrush steppe ecosystems in south-central Wyoming. Net nitrate production, measured in laboratory incubations, was highest in the ecosystem type dominated by Artemisia tridentata ssp. vaseyana, especially early in the growing season. Fluxes of nitrous oxide, measured in closed chambers and analyzed by gas chromatography, also tended to be higher in the same type, but only for short periods in the spring. Thereafter, all nitrous oxide fluxes were low and did not differ consistently among types. Estimated average annual fluxes for three Artemisia ecosystem types (dominated by Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, and Artemisia nova) were 0.32, 0.23 and 0.13 kg N₂O-N ha^–1 y^–1 repsectively. Average annual flux, weighted by the areal extent of these and other vegetation types in the region, was approximately 0.21 kg N₂O-N ha^–1y^–1. Assuming this landscape is representative of sagebrush steppe, we calculate a flux of 9.5 × 10⁹ g y^–1 of N₂O-N from U.S. sagebrush steppe, and a flux of 1.1 × 10¹¹ g y^–1 of N₂0-N from analogous desert and semi-desert shrublands of the world.     

Attractiveness of the male Acheta domesticus calling song to females

1. Most crickets first demonstrated positive phonotaxis to 65 dB CSs having a 53-62 ms SP by day 3 following the imaginal molt (Fig. 3B). The onset of copulatory readiness occurred on average at 3.2 days. 2. The attractive range of SPs for most females became progressively broader as they aged (Fig. 4). Three to 4-day-old females were attracted to a smaller number of CS SPs than were 20-21 day old females (Fig. 4). 3. Older, less selective females did not typically respond to the same range of CS SPs (Fig. 6). However, they were more likely to respond to some SPs (especially 50 ms) than to others (Fig. 7). 4. The phonotactic threshold decreased from 95 dB or greater on day 0 to a mean of 55 dB by day 3, during a period of increasing JHIII biosynthesis, and thereafter remained at that level (Fig. 8). 5. During a period of maximal JHIII production, 3-5 day-old females usually responded to 4 of the 7 SPs presented (Fig. 8). Females older than 12 days were unselective for CS SP, and JHIII synthesis remained at a level below the peak production on day 4 (Fig. 8). 6. Older females, that were unselective for CS SP, became as selective as 3 to 5-day-old females within 4 days of topical application of JHIII (Figs. 9-11).     

On the role of subunit III in proton translocation in cytochromec oxidase

Mammalian mitochondrial cytochromec oxidase catalyzes the transfer of electrons from ferrocytochromec to molecular oxygen in the respiratory chain, while conserving the energy released during its electron transfer reactions by the vectorial movement of protons across the inner membrane of the mitochondrion. The protein domain that translocates the protons across the membrane is currently unknown. Recent research efforts have investigated the role of one of the transmembrane subunits of the enzyme (III,M _r 29,884) in the vectorial proton translocation reaction. The data that favor subunit III as integral in vectorial proton translocation as well as the data that support a more peripheral role for subunit III in proton translocation are reviewed. Possible experimental approaches to clarify this issue are presented and a general model discussed.     

Floral evolution and phylogeny in the tribeThelymitreae (Orchidaceae: Neottioideae)

The Australian orchid tribeThelymitreae, composed ofCalochilus, Epiblema, andThelymitra, is unique in theOrchidaceae because of the presence of a mitra or staminodal complex. Evidence from floral structure suggests thatEpiblema andThelymitra are sister genera and thatCalochilus is derived from aThelymitra ancestor. A Gene Pool Vortex model and a hypothetical phylogeny illustrate that introgressive hybridization, allopatry, and long distance dispersal have played a major role in the evolution of the tribe. Pollination and hybridization in the tribe are discussed with major emphasis on floral mimicry.     

Halimeda bioherms along an open seaway: Miskito Channel,Nicaraguan Rise,SW Caribbean Sea

A recent research cruise to examine small, detached carbonate platforms situated on the Nicaraguan Rise in the SW Caribbean Sea has revealed the presence of numerous Halimeda bioherms. Based upon interpretations from seismic reflection data some exceed 140 m in relief. This is the first documented occurrence of these green-algal buildups in the Caribbean/Bahama Bank region. The Halimeda bioherms form a nearly continuous band that borders the margins of the Miskito Channel—a shallow, open, 125 km long seaway. This 220 m deep channel bisects the Miskito Bank which is a major carbonate shelf. In seismic profile the bioherms appear acoustically soft and reveal a local relief of 20–30 m. Tops of these features lie in about 40–50 m of water. Samples from dredge hauls are coarse, poorly cemented packstones/grainstones which are dominated by largely unbroken, disarticulated Halimeda segments set in a poorly sorted sandy matrix. Exposed surfaces were stained brown. Very little living material was brought up in the dredges. The significance of these bioherms and their full extent in the Caribbean are not understood. Undoubtedly, further study will provide important answers concerning their role in the geologic development of Caribbean carbonate platforms.