A 460-kb DNA Sequence of the Escherichia coli K-12 Genome Corresponding to the 40.1-50.0 min Region on the Linkage Map

The 465,813 base pair sequence corresponding to the 40.1–50.0min region on the genetic map of Escherichia coli K-12 (W3110)was determined. Analysis of the sequence revealed that thisregion contained at least 466 potential open reading frames,of which 187 (40%) were previously reported, 105 (23%) werehomologous to other known genes, 103 (22%) were identical orsimilar to hypothetical genes registered in databases, and theremaining 71 (15%) did not show a significant similarity toany other gene. At the 45.2–46.0 min region, we founda very large cluster of about 30 genes, whose functions areinvolved in the biosynthesis of polysaccharides as the componentsof outer membranes. In addition, we identified anew asn-tRNAgene, designated asnW, between the asnT and asnU genes and anew lysogenic phage attachment site as the cis-element.     

Comparison of properties of leaf and root glutathione reductases from spinach

Glutathione reductase (GR; EC 1.6.4.2) was purified from spinach roots (rGR) to homogeneity in terms of SDS-PAGE, and its properties were compared with those of the enzyme from spinach leaves (IGR). The two enzymes had similar native molecular (118000) and subunit masses (58000) and immunochemical properties, but different pH optima (ca pH 7.8 for IGR, ca pH 7.2 for rGR) and amino acid compositions. Peptide maps of two GRs showed that they differed from each other. The N-terminal amino acid of the IGR was glycine and that of the rGR was blocked. The partial amino acid sequence of the N-terminal region of the IGR was determined to the 11 th residue and it was found that the sequence of 8 amino acids of the IGR had 100% homology with that of the putative chloroplast GR from Arabidopsis and pea.     

Particle selectivity of pelagic tintinnid agglutination

Scanning electron microscopic observation reveals that several agglutinated, pelagic tintinnid taxa apparently possess a capability of incorporating specific mineral grains, such as monospecific coccoliths, for their loricae. Since the ocean water generally contains other coccolith taxa, as well as diatoms and clays, it seems possible that the tintinnids can single out a particular coccolithophore species from the variety of suspended matter for their loricae-building.     

A Supply of Nitrogen Causes Increase in the Level of NADH-Dependent Glutamate Synthase Protein and in the Activity of the Enzyme in Roots of Rice Seedlings

When rice seedlings, after the growth for 26 days in water alone,were transferred to nutrient medium contained 1 mM NH₄Cl, thelevel of NADH-dependent glutamate synthase (GOGAT) protein andthe activity of the enzyme increased more than 10-fold in root,but not in shoots. Both the level of the protein and the activityreached a maximum within 24 h. NH₄Cl was effective at concentrationsas low as 50 µM. A supply of either 1 mM NaNO₃ or 0.5mM NH₄NO₃ also caused such increases, but NHa₄Cl was most effective.A supply of glutamine or glutamate was less effective. The increasewas specific to NADH-GOGAT and little change was observed inthe levels of ferredoxin-GOGAT and glutamine synthetase isoproteinsin roots. These inducible increases in the levels of NADH-GOGATprotein and in its activity were greater in the root-tip regionthan at the base of the root. Both 6-methylpurine and cycloheximidecompletely inhibited the effects of NH₄Cl. Moreover, the mRNAfor NADH-GOGAT in rice roots accumulated markedly within 12h of the start of a supply of NH₄Cl. A possible role for therapid response of NADH-GOGAT to a supply of NH₄C1 is discussed. (Received May 18, 1995; Accepted July 10, 1995)