Pathway of acetate assimilation in autotrophic and heterotrophic methanococci.

The autotroph Methanococcus maripaludis contained high levels of acetate-coenzyme A ligase, pyruvate synthase, pyruvate, water dikinase, pyruvate carboxylase, and the enzymes of the incomplete reductive tricarboxylic acid cycle. Phosphoenolpyruvate carboxykinase, citrate synthase, and isocitrate dehydrogenase were not detected. In contrast, the heterotroph Methanococcus sp. strain A3 contained acetate kinase, and acetate coenzyme A ligase was virtually absent.     

Genetic and Physical Mapping of the Mcra (Rgla) and Mcrb (Rglb) Loci of Escherichia Coli K-12

We have genetically analyzed, cloned and physically mapped the modified cytosine-specific restriction determinants mcrA (rglA) and mcrB (rglB) of Escherichia coli K-12. The independently discovered Rgl and Mcr restriction systems are shown to be identical by three criteria: 1) mutants with the RglA- or RglB- phenotypes display the corresponding McrA- or McrB- phenotypes, and vice versa; 2) the gene(s) for RglA and McrA reside together at one locus, while gene(s) for RglB and McrB are coincident at a different locus; and 3) RglA+ and RglB+ recombinant clones complement for the corresponding Mcr-deficient lesions. The mcrA (rglA) gene(s) is on the excisable element e14, just clockwise of purB at 25 min. The mcrB (rglB) gene(s), at 99 min, is in a cluster of restriction functions that includes hsd and mrr, determinants of host-specific restriction (EcoK) and methyladenine-specific restriction respectively. Gene order is mcrB-hsdS-hsdM-hsdR-mrr-serB. Possible models for the acqusition of these restriction determinants by enteric bacteria are discussed.     

Have the bloody cells gone to our heads?

Recent studies have shown that cells expressing neuronal antigens can be derived from a bone marrow transplant. A new report lends support to and extends these previous results by presenting compelling morphological evidence for the generation and integration of highly differentiated bone marrow-derived neurons.     

Active transport of amino acids in Thiobacillus thioparus is a low-affinity process.

A method for the isolation of amino acid auxotrophs of Thiobacillus thioparus is described. Characterization of a leucine auxotroph indicated that leucine biosynthesis in T. thioparus was not different from that of heterotrophic bacteria. T. thioparus cells accumulated amino acids via an active mechanism. Kt values of amino acid transport were between 15 and 330 microM, and Vmax values were 200 to 350 pmol min-1 mg of protein-1. Amino acid transport was carried out by a limited number of systems, each responsible for the uptake of several amino acids. Amino acid auxotrophs of T. thioparus exhibited transport and growth properties similar to those of transport-deficient mutants of heterotrophs which lost the high-affinity, but retained the low-affinity, amino acid transport systems.     

The Stress Hormone Corticosterone Increases Synaptic ��-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors via Serum- and Glucocorticoid-inducible Kinase (SGK) Regulation of the GDI-Rab4 Complex

Corticosterone, the major stress hormone, plays an important role in regulating neuronal functions of the limbic system, although the cellular targets and molecular mechanisms of corticosteroid signaling are largely unknown. Here we show that a short treatment of corticosterone significantly increases α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated synaptic transmission and AMPAR membrane trafficking in pyramidal neurons of prefrontal cortex, a key region involved in cognition and emotion. This enhancing effect of corticosterone is through a mechanism dependent on Rab4, the small GTPase-controlling receptor recycling between early endosome and plasma membrane. Guanosine nucleotide dissociation inhibitor (GDI), which regulates the cycle of Rab proteins between membrane and cytosol, forms an increased complex with Rab4 after corticosterone treatment. Corticosterone also triggers an increased GDI phosphorylation at Ser-213 by the serum- and glucocorticoid-inducible kinase (SGK). Moreover, AMPAR synaptic currents and surface expression and their regulation by corticosterone are altered by mutating Ser-213 on GDI. These results suggest that corticosterone, via SGK phosphorylation of GDI at Ser-213, increases the formation of GDI-Rab4 complex, facilitating the functional cycle of Rab4 and Rab4-mediated recycling of AMPARs to the synaptic membrane. It provides a potential mechanism underlying the role of corticosteroid stress hormone in up-regulating excitatory synaptic efficacy in cortical neurons.