Fluorescence detection in automated DNA sequence analysis

We have developed a method for the partial automation of DNA sequence analysis. Fluorescence detection of the DNA fragments is accomplished by means of a fluorophore covalently attached to the oligonucleotide primer used in enzymatic DNA sequence analysis. A different coloured fluorophore is used for each of the reactions specific for the bases A, C, G and T. The reaction mixtures are combined and co-electrophoresed down a single polyacrylamide gel tube, the separated fluorescent bands of DNA are detected near the bottom of the tube, and the sequence information is acquired directly by computer.     

New 'phantom' dinoflagellate is the causative agent of major estuarine fish kills.

A worldwide increase in toxic phytoplankton blooms over the past 20 years has coincided with increasing reports of fish diseases and deaths of unknown cause. Among estuaries that have been repeatedly associated with unexplained fish kills on the western Atlantic Coast are the Pamlico and Neuse Estuaries of the southeastern United States. Here we describe a new toxic dinoflagellate with 'phantom-like' behaviour that has been identified as the causative agent of a significant portion of the fish kills in these estuaries, and which may also be active in other geographic regions. The alga requires live finfish or their fresh excreta for excystment and release of a potent toxin. Low cell densities cause neurotoxic signs and fish death, followed by rapid algal encystment and dormancy unless live fish are added. This dinoflagellate was abundant in the water during major fish kills in local estuaries, but only while fish were dying; within several hours of death where carcasses were still present, the flagellated vegetative algal population had encysted and settled back to the sediments. Isolates from each event were highly lethal to finfish and shellfish in laboratory bioassays. Given its broad temperature and salinity tolerance, and its stimulation by phosphate enrichment, this toxic phytoplankter may be a widespread but undetected source of fish mortality in nutrient-enriched estuaries.     

Sarcoplasmic reticulum contains adenine nucleotide-activated calcium channels

Rapid calcium efflux from the sarcoplasmic reticulum (SR) is a necessary step in excitation-contraction coupling in skeletal muscle and is thought to be mediated by a calcium channel. Calcium efflux has been studied in fragmented SR vesicles by radioisotope efflux and fluorescence measurements. Several laboratories have reported that adenine nucleotides can stimulate calcium efflux from SR. In recent reports, Ca2+ release with a first-order rate constant as high as 100 s-1 has been observed for nucleotide-stimulated Ca2+ release from SR vesicles. Also, radioisotope efflux was blocked by Mg2+ and micromolar concentrations of the polycationic dye, ruthenium red. These high rates of transport are difficult to reconcile with a mechanism other than passive diffusion through a nucleotide-activated 'calcium release channel'. Using the fusion technique for inserting SR proteins into planar lipid bilayers, we report here single-channel recordings of calcium release channels from purified 'heavy' SR membranes. Channels have been identified on the basis of their activation by adenine nucleotides, blockade by ruthenium red, and selectivity for divalent cations. Surprisingly, the channel studied here exhibits an unusually large conductance of 170 pS in 50 mM Ba2+ while still being capable of discriminating against monovalent cations by a permeability ratio, P(Ba)/P(Cs) = 11.4.     

Effects of the adenylate cyclase activator forskolin and its inactive derivative 1,9-dideoxyforskolin on insect cytochrome P-450 dependent steroid hydroxylase activity.

The adenylate cyclase activator forskolin and its pharmacologically inactive derivative 1,9-dideoxyforskolin were found to inhibit in a dose-dependent fashion the ecdysone 20-monooxygenase activity associated with wandering stage larvae of Drosophila melanogaster and fat body and midgut from last instar larvae of the tobacco hornworm, Manduca sexta. The concentrations of these labdane diterpenes required to elicit a 50% inhibition of the cytochrome P-450 dependent steroid hydroxylase activity in the insect tissues ranged from approximately 5 x 10(-6) to 5 x 10(-4) M.     

The synthesis of stereoselectively labelled porphobilinogen and its incorporation into protoporphyrin-IX

Summary 11-(R)-²H porphobilinogen, stereospecifically labelled with deuterium in the aminomethylene group has been incorporated into protoporphyrin-IX by haemolysates of chicken erythrocytes. High field NMR spectroscopy confirms that the overall biochemical process is stereospecific, deuterium being retained at the -, -and -meso positions and lost from the -meso position.27 August 1986     

A beautiful sea: P. A. M. Dirac's epistemology and ontology of the vacuum

This paper charts P.A.M. Dirac's development of his theory of the electron, and its radical picture of empty space as an almost-full plenum. Dirac's Quantum Electrodynamics famously accomplished more than the unification of special relativity and quantum mechanics. It also accounted for the ‘duplexity phenomena’ of spectral line splitting that we now attribute to electron spin. But the extra mathematical terms that allowed for spin were not alone, and this paper charts Dirac's struggle to ignore or account for them as a sea of strange, negative-energy, particles with positive ‘holes’. This work was not done in solitude, but rather in exchanges with Dirac's correspondence network. This social context for Dirac’s work contests his image as a lone genius, and documents a community wrestling with the ontological consequences of their work. Unification, consistency, causality, and community are common factors in explanations in the history of physics. This paper argues on the basis of materials in Dirac's archive that --- in addition --- mathematical beauty was an epistemological factor in the development of the electron and hole theory. In fact, if we believe that Dirac's beautiful mathematics captures something of the world, then there is both an epistemology and an ontology of mathematical beauty.     

The naturalism of the sciences

The sciences are characterized by what is sometimes called a “methodological naturalism,” which disregards talk of divine agency. In response to those who argue that this reflects a dogmatic materialism, a number of philosophers have offered a pragmatic defense. The naturalism of the sciences, they argue, is provisional and defeasible: it is justified by the fact that unsuccessful theistic explanations have been superseded by successful natural ones. But this defense is inconsistent with the history of the sciences. The sciences have always exhibited what we call a domain naturalism. They have never invoked divine agency, but have always focused on the causal structure of the natural world. It is not the case, therefore, that the sciences once employed theistic explanations and then abandoned them. The naturalism of the sciences is as old as science itself.