Exposure of human lymphocytes to ionizing radiation reduces mutagenesis by subsequent ionizing radiation

The effect of prior incubation with [3H]thymidine on survival and mutagenesis after X-irradiation of human lymphocytes was studied by incubating lymphocytes with 0.001-1.0 mu Ci/ml [3H]thymidine for 6 h at 37 degrees C and then irradiating with 150 or 300 rad. Survival was measured using lymphocyte cloning and mutagenesis was measured using 6-thioguanine selection to detect clones mutated at the hypoxanthine phosphoribosyltransferase locus. [3H]Thymidine alone had no effect on survival or mutagenesis and X-radiation alone produced the expected decrease in survival and increase in mutations. [3H]Thymidine prior to X-radiation had no effect on lethality of X-radiation but at concentrations of 0.1 and 1.0 mu Ci/ml produced a significant decrease in the number of mutations induced after both 150 and 300 rad. The results suggest that ionizing radiation, produced by disintegration of 3H, reduces the mutagenic effect of a subsequent exposure to ionizing radiation by induction of a system which prevents or repairs a restricted class of radiation damage.     

Crystal and solution structures of the oligonucleotide d(ATGCGCAT)2: a combined X-ray and NMR study.

A combined crystal-structure determination and NMR analysis of the octanucleotide d(ATGCGCAT)2 is reported. The X-ray analysis shows that the structure is A-form duplex in crystal state. The NMR study shows that in solution this sequence is B-type. The conformational results from each technique are presented in detail. The implications of these findings in terms of conformational flexibility and ligand binding are discussed.     

Structure-function analysis of interleukin-5 utilizing mouse/human chimeric molecules.

Interleukin-5 (IL5) is a T cell derived glycoprotein that stimulates eosinophil production and activation. In the mouse, but apparently not in the human, it is active on B cells. The murine and human IL5 polypeptides exhibit 70% sequence similarity and yet display distinct species-specific activity. Whilst mouse and human IL5 are equally active in human cell assays, human IL5 is 100-fold less active than murine IL5 in mouse cell assays. Two restriction sites were utilized to divide the human and mouse sequences into three fragments. Hybrid molecules consisting of all combinations of these fragments were constructed and expressed. In the human cell assays [using bone marrow or the erythroleukaemic cell line (TF-1)] all the hybrid proteins generated activity comparable to that of the human and mouse IL5. This implies that replacing different domains does not result in detrimental effects to the tertiary structure of the molecule. In the mouse cell assays [using bone marrow or the pro-B cell line (B13)] the hybrids clearly identified the importance of residues in the C terminus for biological activity. The changing of only eight residues in this region of human IL5, to those of mouse IL5, resulted in the hybrid producing biological activity comparable to mouse IL5. In addition, competition binding assays showed that this region probably interacts with the receptor.     

Cloning and analysis of the sfrB (sex factor repression) gene of Escherichia coli K-12.

The sfrB gene of Escherichia coli K-12 and the rfaH gene of Salmonella typhimurium LT2 are homologous, controlling expression of the tra operon of F and the rfa genes for lipopolysaccharide synthesis. We have determined a restriction map of the 19-kilobase ColE1 plasmid pLC14-28 which carries the sfrB gene of E. coli. After partial Sau3A digestion of pLC14-28, we cloned a 2.5-kilobase DNA fragment into the BamHI site of pBR322 to form pKZ17. pKZ17 complemented mutants of the sfrB gene of E. coli and the rfaH gene of S. typhimurium for defects of both the F tra operon and the rfa genes. pKZ17 in minicells determines an 18-kilodalton protein not determined by pBR322. A Tn5 insertion into the sfrB gene causes loss of complementing activity and loss of the 18-kilodalton protein in minicells, indicating that this protein is the sfrB gene product. These data indicate that the sfrB gene product is a regulatory element, since the single gene product elicits the expression of genes for many products for F expression and lipopolysaccharide synthesis.     

N.m.r. studies of the disulphated disaccharide obtained by degradation of bovine lung heparin with nitrous acid

The disulphated disaccharide IdoA(2SO3)-anManOH(6SO3) was prepared from bovine lung heparin by treatment with nitrous acid followed by borohydride reduction. The 1H- (400 MHz) and 13C-n.m.r. (100 MHz) spectra of this disaccharide derivative have been assigned completely using homonuclear spin-decoupling experiments, 13C-1H correlations, and a COSY-45 two-dimensional homonuclear correlation experiment. The 3JH,H values show that the IdoA(2SO3) residue exists in a single conformation throughout the temperature range 20-90 degrees.     

Transformation of Salmonella typhimurium with plasmid DNA: differences between rough and smooth strains.

Lipopolysaccharide-defective mutants of Salmonella typhimurium were transformed by plasmid DNA with a Ca2+ treatment method. Only those mutants with an Rc or Rd2 chemotype, due to galE or rfaF mutations, respectively, gave efficiencies greater than 10(5) transformants per microgram of DNA, frequencies 8- to 630-fold higher than with smooth strains or other rough mutants.     

Distribution Coding in the Visual Pathway

Although a variety of types of spike interval histograms have been reported, little attention has been given to the spike interval distribution as a neural code and to how different distributions are transmitted through neural networks. In this paper we present experimental results showing spike interval histograms recorded from retinal ganglion cells of the cat. These results exhibit a clear correlation between spike interval distribution and stimulus condition at the retinal ganglion cell level. The averaged mean rates of the cells studied were nearly the same in light as in darkness whereas the spike interval histograms were much more regular in light than in darkness. We present theoretical models which illustrate how such a distribution coding at the retinal level could be “interpreted” or recorded at some higher level of the nervous system such as the lateral geniculate nucleus. Interpretation is an essential requirement of a neural code which has often been overlooked in modeling studies. Analytical expressions are derived describing the role of distribution coding in determining the transfer characteristics of a simple interaction model and of a lateral inhibition network. Our work suggests that distribution coding might be interpreted by simply interconnected neural networks such as relay cell networks, in general, and the primary thalamic sensory nuclei in particular.