TRANSCRIPTIONAL ACTIVITIES OF THE CHLOROPLAST-NUCLEI AND PROPLASTID-NUCLEI ISOLATED FROM TOBACCO EXHIBIT DIFFERENT SENSITIVITIES TO TAGETITOXIN - IMPLICATION OF THE PRESENCE OF DISTINCT RNA-POLYMERASES

We examined the effects of tagetitoxin, a potent inhibitor of RNA poly merases from chloroplasts and Escherichia coli, on the transcriptional activities of chloroplast- and proplastid-nuclei (nucleoids) isolated from mature tobacco (Nicotiana tabacum L,) leaves and cultured tobacc o cells (line BY-2), respectively. Transcription by the isolated chlor oplast-nuclei was effectively inhibited by tagetitoxin (95-99% reducti on at 10 mu M tagetitoxin), but transcription by the isolated proplast id-nuclei was only partially inhibited (40-50% reduction) by this comp ound. Southern hybridization experiments revealed that the transcripti on of various plastid genes (psbA, atpA, rpoB, psaA/B, atpB, rbcL, pet B, rpl16, and rrn23) was sensitive to tagetitoxin in the isolated chlo roplast-nuclei, whereas the transcription of the same genes was relati vely resistant to this compound in the isolated proplastid-nuclei. The se results suggest that; (i) distinct RNA polymerase activities with d ifferent sensitivities to tagetitoxin are present in plastids, (ii) a tagetitoxin-sensitive RNA polymerase is the major RNA polymerase in ch loroplasts whereas a tagetitoxin-insensitive enzyme is major in propla stids, and (iii) both RNA polymerases can transcribe various plastid g enes.