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Identification of two classes of Rhizobium phaseoli genes required for melanin synthesis, one of which is required for nitrogen fixation and activates the transcription of the other (1987)

Borthakur, D. ; Lamb, J. W. ; Johnston, A. W. B.

Springer

Molecular genetics and genomics 207 (1987), S. 155-160

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ISSN: 1617-4623

Keywords: Gene regulation ; Melanin synthesis ; Nitrogen fixation ; Phaseolus beans ; Rhizobium phaseoli

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The symbiotic plasmid pRP2JI of Rhizobium phaseoli strain 8002 was shown to contain two separate regions of DNA which are required and sufficient for the synthesis of the pigment melanin. One of these regions containing the class II mel gene(s) was located to other genes involved in nodulation and in nitrogen fixation. Mutations in this region abolished both the ability to synthesize melanin and to fix nitrogen in Phaseolus bean root nodules. Mutations in the other, unlinked region, containing class I mel gene(s), also abolished melanin synthesis but did not affect symbiotic nitrogen fixation. Transcriptional fusions between the class I mel gene and the Escherichia coli lacZ gene were constructed and it was demonstrated that the class II mel gene(s) activated their transcription in free-living culture. Further, strains containing the cloned regulatory class II gene(s) synthesized melanin when growing in minimal medium, in contrast to wild-type strains which became pigmented only in complete medium containing yeast extract and tryptone. It was shown by hybridization experiments that the regulatory mel gene was closely linked to or may correspond to the regulatory nifA gene; a fragment of R. phaseoli DNA which included the class II gene(s) of R. phaseoli hybridized to a previously identified nifA-like gene of R. leguminosarum, the species that nodulates peas.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00331503

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Adsorption of N-phenylglycine on hydroxyapatite: Role in the bonding procedure of a restorative resin to dentin (1987)

Misra, D. N. ; Johnston, A. D.

Hoboken, NJ : Wiley-Blackwell

Journal of Biomedical Materials Research 21 (1987), S. 1329-1339

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ISSN: 0021-9304

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine , Technology

Notes: The adsorption of N-phenylglycine (NPG) onto synthetic hydroxyapatite from ethanol solutions was studied to elucidate the role of surface-active moieties in determining the character of adsorption, and to explore the role of NPG in a bonding procedure of restorative resin to dentin. The adsorption isotherm of N-phenylglycine is reversible (and Langmuirian) from ethanol (99.8%). At maximum adsorption the phenyl rings of the adsorbed molecules lie flat on the surface and the carboxylate oxygens and amino nitrogens are anchored to the surface. The N-phenylglycine serves as an amine accelerator since the peroxide containing monomer polymerizes with the adsorbate-covered apatite. The diametral tensile strength of this composite is approximately equal to the composite filled with untreated apatite. The role of various factors contributing to adhesive strength in the bonding procedure is also discussed.

Additional Material: 2 Ill.