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At least 991 records · Page 55Linked to original sources
PubMed1971

Adenosine triphosphate-dependent synthesis of biologically active DNA by azide-poisoned bacteria.

Nonviable cells of Bacillus subtilis, when made permeable by treatment under controlled conditions with nonionic detergent, can be shown to replicate DNA normally and to repair certain regions of the chromosome. The former process is stimulated by ATP in the presence of dATP, dCTP, dGTP, and dTTP. The product, a result of semiconservative replication, is biologically active; synthesis of the newly-formed regions of the chromosome appears to be sequential.

Adenosine Triphosphate↗
PubMed1993

Orientation of the LexA DNA-binding motif on operator DNA as inferred from cysteine-mediated phenyl azide crosslinking.

To address the question how the recognition helix of the LexA repressor is positioned within the major groove of operator DNA we have applied a site-specific photocrosslinking approach using a LexA mutant repressor (LexA-C52) that harbors a single cysteine side chain in position 52, close to the COOH terminus of helix 3. The LexA-C52 mutant repressor has been purified and modified site-specifically with the photoreactive azido compound 4-azidophenacyl bromide, giving rise to LexA-C52*. Here we show that LexA-C52* may be selectively photocrosslinked with two adjacent bases within each operator half-site. The crosslinked bases are located, respectively, 10 and 11 base pairs from the dyad axis of the operator. The crosslinking data imply that the LexA recognition helix is oriented opposite to what is generally observed for helix-turn-helix proteins and that this helix should form a steeper angle with respect to the plane of the base pairs than is observed for standard helix-turn-helix proteins.

Azides↗
PubMed1973

Somatic crossing over in Glycine max (L.) Merrill: mutagenicity of sodium azide and lack of synergistic effect with caffeine and mitomycin C.

Glycine max (soybean) is one angiosperm which lends itself to the study of somatic crossing over. This is made possible because some varieties have gene combinations Y(11)Y(11), Y(11)y(11) and y(11)y(11) in the segregating populations from Y(11)y(11) plants. The gene in question is responsible for chlorophyll synthesis. The Y(11)Y(11) plants have dark green leaves, Y(11)y(11) are light green and y(11)y(11) plants are golden yellow. The heterozygous plants have dark green, yellow and dark green-yellow (double) spots on the leaves of the untreated control material, whereas the two homozygotes are almost always devoid of somatic sectoring. Application of caffeine, or mitomycin C, to the seeds increased the frequency of double, dark green and yellow spots on the Y(11)y(11) background. Possibly, some dark green or yellow spots originate by failure of one of the two components of what might start as a double spot due to somatic crossing over. The application of NaN(3) increases the frequency of dark green or yellow spots, almost exclusively. The two spots increase in equal frequency. The y(11)y(11) plants so treated do not have any light green sectors, but dark green, Y(11)Y(11), plants do develop a few light green or very dark green spots. The data indicate that NaN(3) is capable of inducing nondisjunction, but does not cause mutations (at this locus), chromosome fragmentations (segmental losses) or somatic crossing over to an appreciable degree. It has previously been shown that caffeine-induced chromosome rejoining in Vicia faba can be inhibited by treating the roots with NaN(3). In the present experiments NaN(3) did not affect the processes of somatic crossing over as induced by caffeine or mitomycin C. The effect was additive. This system offers advantages for studying chemical mutagens in that somatic crossing over, point mutations, segmental losses through chromosome breakage and nondisjunction can all be studied in a single treatment to the seeds.

Azides↗
PubMed1993

Site-directed cross-linking studies on the E. coli tRNA-ribosome complex: determination of sites labelled with an aromatic azide attached to the variable loop or aminoacyl group of tRNA.

tRNA(Phe) from E. coli, modified with the photoreactive label N-(p-azidobenzoyl)-glycine (ABG) either at the naturally occurring nucleotide 3-(3-amino-3-carboxy-propyl) uridine (acp3U47) or the alpha-amino group of Phe-tRNA(Phe), was bound nonenzymatically to 70S ribosomes in the presence of poly (U) or short synthetic mRNA molecules prepared by T7 transcription. The noncovalent complexes were subjected to a mild ultraviolet irradiation treatment and the sites of photo-incorporation were analysed. When the photo-affinity label was attached to the aminoacyl group cross-linking was observed from both A- and P-site bound tRNA and involved exclusively the 50S subunit. In both cases the major target of cross-linking was a single site in 23S RNA, localized to position A-2439. A lower yield of cross-linking to L27 from both P- and A-sites was also observed. In contrast, cross-linking from the acp3U47 derivative was specific for P-site bound tRNA and involved mainly (but not exclusively) the 50S subunit. In this case rRNA and ribosomal protein were labelled in approximately equal yields, the sites of cross-linking involving A-2309 in 23S RNA and L33. These results are discussed in the light of our present knowledge concerning the structural arrangement of the tRNA-ribosome complex.

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