Mycobacterium tuberculosis infection continues to cause substantial human suffering. New chemotherapeutic strategies, which require insight into the pathways essential for M. tuberculosis pathogenesis, are imperative. We previously reported that depletion of the CarD protein in mycobacteria compromises viability, resistance to oxidative stress and fluoroquinolones, and pathogenesis. CarD associates with the RNA polymerase (RNAP), but it has been unknown which of the diverse functions of CarD are mediated through the RNAP; this question must be answered to understand the CarD mechanism of action. Herein, we describe the interaction between the M. tuberculosis CarD and the RNAP ␤ subunit and identify point mutations that weaken this interaction. The characterization of mycobacterial strains with attenuated CarD/RNAP ␤ interactions demonstrates that the CarD/ RNAP ␤ association is required for viability and resistance to oxidative stress but not for fluoroquinolone resistance. Weakening the CarD/RNAP ␤ interaction also increases the sensitivity of mycobacteria to rifampin and streptomycin. Surprisingly, depletion of the CarD protein did not affect sensitivity to rifampin. These findings define the CarD/RNAP interaction as a new target for chemotherapeutic intervention that could also improve the efficacy of rifampin treatment of tuberculosis. In addition, our data demonstrate that weakening the CarD/RNAP ␤ interaction does not completely phenocopy the depletion of CarD and support the existence of functions for CarD independent of direct RNAP binding.

Tin-119 chemical shifts in 59 organo-tin compounds have been obtained by 1H-{119Sn) double-resonance experiments. This technique offers considerable advantages in precision and sensitivity over the conventional method. Correlations with electronegativity of the groups attached to tin are noted, and it is concluded that the prr-dr overlap may be important in halogen compounds. Dispersion forces also appear to affect the shifts when bulky polarizable groups are present. High-resolution INDOR spectra are presented, and are used to confirm certain structures, and to estimate otherwise inaccessible couping constants.Two lists of l19Sn chemical shifts appear in the literature,lY2 the values in both being obtained by direct observation of the l19Sn resonance in a spectrometer operating at a suitable frequency. The second coinpil-ation appeared when our work was still in progress, but there is little overlap in the selection of compounds.Three isotopes of tin have spin Q, but attention is usually confined to lI9Sn, since this is the most abundant

Trimethyltin chloride-triphenylphosphineacetylmethylene is 0 rather than C-bonded. MERCURY (11) halides react with cc-carbonyl phosphorusylides to give stable C-mercurated phosphonium sa1ts.l

of furanocbomones. Can. 9. Biochern. 49,[964][965][966][967][968][969][970].Radioactive khellin, visnagin, and visarnminol were recovered from Anarni oisnaga plants fed [I-14C]-acetate. A trapping experiment with 5,7-dihydroxy-2-methylchromone indicated that this compound was formed from acetate in the plant. It was then prepared labelled with I4C and 'H and administered to shoots, demonstrating its conversion to visarnrninol and furancdshomones. A biosynthetic pathway is proposed: acetate + 5,7-dihydroxy-2-methylchron10ne -+ peu~nin++visamminol++visnagin and khellin.The gas chromatography of some A. visnaga constituents is described. The furamocoumarins xanthotoxin and isopimpinellin were shown to be present in the plant.Administration of labelled 5,7-dihydsoxy-Zrnethylchromone to shoots of Angelica archangelica resulted in the elaboration of labelled furanochrsmones, suggesting that the furan moiety of furamochromones and fwamocoumarins may be formed via similar if not identical enzyme systems. HARRISON, P. G., BAILEY, B. K., et STECK, W. Biosynthesis of furanochromones. Can. J. Biochem. 49, 964-970 (1971).Apr6s ingestion de [I-14C] acktate par des plants d9Ammi visnaga, nous avons recouvrk de la radioactivitb dans la kheIline, la visnagine et Ie visamminol. Une experience de trappage dkmontre que dans 8 wtte plante, la $7-dihydroxy-2-mCthylc~omone est formke h partir de l'acbtate. Nous I'avons alors marquke avec le I4C et le 'H et nous l'avons administree ii des pousses pour demontrer sa conversion en visamminol et en furanochrsmones. Voici la route biosynthetique proposie: acbtate-+5,7-dihydroxy-2-m~thylchromone-+peucenine++visarnminol++visnagine et khelline.Nous decrivons la chromatographie en phase gazeuse de quelques constituants d'A. oisnaga. Ees furanocoumarines xanthotoxine et isopimpinelline, sont prtsentes dans la plamte. L'administration de 5,7-dihydroxy-2-m$thylchromone masquk a des pousses d9Angelisa archangelica entraine 1'elaboration de furanmhromones marquees. II semble done que la fraction furame des furanochromones et des furanocoumarines wit formde par des systkmes enzymatiques semblables sinon identiques.INRCC No. 11993. 2NRCC summer student 1970. Present address :

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