TRANSCRIPTION AND EDITING OF CYTOCHROME OXIDASE-II RNAS IN TRYPANOSOMA-CRUZI

The cytochrome oxidase subunit II (COII) gene is one of the maxicircle cryptogenes of kinetoplastids whose primary transcripts are sometimes modified by RNA editing to produce mature mRNAs. We determined the se quence of the COII gene in three strains of Trypanosoma cruzi (Y, Corp us Christi, and Tulahuen) and examined its developmental expression. C omparison of the RNA and DNA sequences encoding COII indicated that in the three strains of T. cruzi, four uridines are inserted in the pre- mRNA at the same positions as they are in the COII pre-mRNAs of Trypan osoma brucei, Leishmania tarentolae, and Crithidia fasciculata. The pu tative guide RNA (gRNA) sequence that serves as a template for the fou r uridine insertions is located in the 3'-untranslated region of the T cruzi COII mRNA. Analysis of editing intermediates demonstrates that the COII gRNA remains attached to the pre-mRNA while participating in the formation of chimeric RNAs. Northern blots used to investigate sta ge-specific expression of the COII gene revealed RNAs of 800 and 900 n ucleotides, similar in size to those present in T brucei. In contrast to the differential expression observed in T. brucei, no difference oc curs between the COII mRNA levels of insect and mammalian stages of T cruzi.