Characterization of Two New Genes, amoR and amoD, in the amo Operon of the Marine Ammonia Oxidizer Nitrosococcus oceani ATCC 19707

Molecular analysis of the amo gene cluster in Nitrosococcus oceani revealed that it consists of five genes, instead of the three known genes, amoCAB. The two additional genes, orf1 and orf5, were introduced as amoR and amoD, respectively. Putative functions of the AmoR and AmoD proteins are discussed.     

Deletion of the trichodiene synthase gene of Fusarium venenatum: two systems for repeated gene deletions.

The trichodiene synthase (tri5) gene of Fusarium venenatum was cloned from a genomic library. Vectors were created in which the tri5 coding sequence was replaced with the Neurospora crassa nitrate reductase (nit3) gene and with the Aspergillus nidulans acetamidase (amdS) gene flanked by direct repeats. The first vector was utilized to transform a nitrate reductase (niaD) mutant of F. venenatum to prototrophy, and the second vector was utilized to confer acetamide utilization to the wild-type strain. Several of the transformants lost the capacity to produce the trichothecene diacetoxyscirpenol and were shown by hybridization analysis to have gene replacements at the tri5 locus. The nit3 gene was removed by retransformation with a tri5 deletion fragment and selection on chlorate. The amdS gene was shown to excise spontaneously via the flanking direct repeats when spores were plated onto fluoroacetamide.     

Biological action and fate of photoaffinity-labelled insulin-receptor complexes

Covalent linking of two photoactivatable insulin derivatives, B2-(2-nitro,4-azidophenylacetyl)-des-PheB1-insulin and B29-(2-nitro,4-azidophenylacetyl)-insulin to viable rat adipocytes gives a system, which contains a fixed stoichiometry between hormone and receptor. The biological signal of prolonged lipogenesis has been used to study several aspects of insulin binding and action: the role of the site of the crosslink between insulin and receptor, recognition of bound photoinsulin by anti-insulin antibodies, the half-life of the biologically active complex, the pH-dependence of the biological signal, and the possible role of internalization. Furthermore, the effect of trypsin on the insulin receptor, as well as the insulin-receptor complex, has been investigated and a refined model of the receptor is presented.     

Determination of the molecular weight of Saccharomyces cerevisiae nuclear DNA

Viscoelastic retardation-time experiments on the DNA released from spheroplasts of the yeast Saccharomyces cerevisiae yield a molecular weight of 2 × 10⁹ for the largest DNA, assuming linear unbranched DNA, and of 4.3 × 10⁹ assuming circular unbranched DNA. Both log and stationary-phase cells give the same results. Comparison of these results with the nuclear DNA content of S. cerevisiae determined by renaturation kinetics suggests that the largest piece of DNA in the yeast nucleus may, at least during part of the cell cycle, consist of from one-fourth to all of the yeast genome.     

Dependence of polynucleotide helix–coil transition theory on the ring closure exponent

Formulas are derived which relate the maximum slope of the helix-coil transition in synthetic polynucleotides to the stacking free energy and to the exponent k in the expression for the probability of ring closure for polymer chains. The exact value of k has not yet been determined. By use of the derived formulas, it is then shown that estimates of the stacking free energy are sensitive enough to the value chosen for k, so that exact values of these energies must await a precise determination of k.     

Radiation inactivation analysis of the A1 adenosine receptor of rat brain. Decrease in radiation inactivation size in the presence of guanine nucleotide

Radiation inactivation analysis of the binding of the A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine to rat brain membranes yielded a radiation inactivation size of 58 kDa. In the presence of GTP gamma S this was reduced to 33 kDa, in good agreement with the size of the ligand-binding subunit detected after photoaffinity labelling. The data indicate that the structural association of A1 adenosine receptors with G-protein components is altered in situ in the presence of guanine nucleotides.