Biosynthesis of deuteriated amino acids byCandida lipolytica

Summary Biosynthesis of a whole series of deuteriated amino acids has been carried out, by cultivation of the yeastCandida lipolytica in an artificial medium composed of a deuterio-alkane, heavy water, water and some mineral salts.Acknowledgments. This work has been carried out with the aid of grants from The Swedish Medical Research Council. Thanks are due to Mr Nils Engström for his skilful technical assistance during the yeast growth, and to Mrs Monica Olsson for the Moore-Stein analysis.     

Partial complementation of a DNA ligase I deficiency by DNA ligase III and its impact on cell survival and telomere stability in mammalian cells

DNA ligase I (LigI) plays a central role in the joining of strand interruptions during replication and repair. In our current study, we provide evidence that DNA ligase III (LigIII) and XRCC1, which form a complex that functions in single-strand break repair, are required for the proliferation of mammalian LigI-depleted cells. We show from our data that in cells with either dysfunctional LigI activity or depleted of this enzyme, both LigIII and XRCC1 are retained on the chromatin and accumulate at replication foci. We also demonstrate that the LigI and LigIII proteins cooperate to inhibit sister chromatid exchanges but that only LigI prevents telomere sister fusions. Taken together, these results suggest that in cells with dysfunctional LigI, LigIII contributes to the ligation of replication intermediates but not to the prevention of telomeric instability.     

Pfiesteria shumwayae kills fish by micropredation not exotoxin secretion

Pfiesteria piscicida and P. shumwayae reportedly secrete potent exotoxins thought to cause fish lesion events, acute fish kills and human disease in mid-Atlantic USA estuaries. However, Pfiesteria toxins have never been isolated or characterized. We investigated mechanisms by which P. shumwayae kills fish using three different approaches. Here we show that larval fish bioassays conducted in tissue culture plates fitted with polycarbonate membrane inserts exhibited mortality (100%) only in treatments where fish and dinospores were in physical contact. No mortalities occurred in treatments where the membrane prevented contact between dinospores and fish. Using differential centrifugation and filtration of water from a fish-killing culture, we produced 'dinoflagellate', 'bacteria' and 'cell-free' fractions. Larval fish bioassays of these fractions resulted in mortalities (60-100% in less than 24 h) only in fractions containing live dinospores ('whole water', 'dinoflagellate'), with no mortalities in 'cell-free' or 'bacteria'-enriched fractions. Videomicrography and electron microscopy show dinospores swarming toward and attaching to skin, actively feeding, and rapidly denuding fish of epidermis. We show here that our cultures of actively fish-killing P. shumwayae do not secrete potent exotoxins; rather, fish mortality results from micropredatory feeding.     

Beta 2-microglobulin restriction of antigen presentation.

Antigens are generally thought to be recognized by cytotoxic T lymphocytes as peptides in the context of class I major histocompatibility proteins complex, which are heterodimers of heavy chains noncovalently associated with beta 2-microglobulin (beta 2m). The highly polymorphic nature of the heavy chains and their resulting ability to present different sets of peptides has presumably evolved to allow potent immune responses against most pathogens. By contrast, the polymorphism of beta 2m is limited; seven alleles are known in the mouse and only one has been identified in humans. beta 2-Microglobulin was consequently thought to have only structural functions: namely, to ensure correct folding of class I molecules and their transport to the cell surface. Although beta 2m is not implicated directly in the formation of the peptide binding site, we report here that it participates in the selection of MHC class I molecule-associated peptides.     

Paraneoplastic myasthenic syndrome IgG inhibits 45Ca2+ flux in a human small cell carcinoma line

Certain cancers exert unexplained remote effects on the nervous system. Small cell carcinoma (SCC) of the lung, a tumour capable of spike electrogenesis and which is of possible neural crest origin, is present in approximately 70% of patients with the Lambert-Eaton myasthenic syndrome (LEMS), a disorder characterized by fatigable muscle weakness. Patients with this syndrome have a defect in the (Ca2+-dependent) quantal release of acetylcholine from motor nerve terminals evoked by a nerve impulse or by high K+ (ref.5), and a decreased number of presynaptic active zone particles. The physiological and morphological features of the syndrome can be transferred to mice by the patients' IgG, consistent with an autoantibody interfering with the function of voltage-dependent Ca2+ channels. Here we demonstrate that K+-induced 45Ca2+ flux in a cultured human SCC line is significantly reduced by LEMS IgG, suggesting that in SCC-LEMS an autoantibody to tumour Ca2+-channel determinants is triggered; its cross-reaction with similar determinants at the motor nerve terminal could lead to the remote neurological syndrome.     

Electronic read-out of a single nuclear spin using a molecular spin transistor

Quantum control of individual spins in condensed-matter devices is an emerging field with a wide range of applications, from nanospintronics to quantum computing. The electron, possessing spin and orbital degrees of freedom, is conventionally used as the carrier of quantum information in proposed devices. However, electrons couple strongly to the environment, and so have very short relaxation and coherence times. It is therefore extremely difficult to achieve quantum coherence and stable entanglement of electron spins. Alternative concepts propose nuclear spins as the building blocks for quantum computing, because such spins are extremely well isolated from the environment and less prone to decoherence. However, weak coupling comes at a price: it remains challenging to address and manipulate individual nuclear spins. Here we show that the nuclear spin of an individual metal atom embedded in a single-molecule magnet can be read out electronically. The observed long lifetimes (tens of seconds) and relaxation characteristics of nuclear spin at the single-atom scale open the way to a completely new world of devices in which quantum logic may be implemented.