MULTIPLE GUIDE RNAS FOR IDENTICAL EDITING OF TRYPANOSOMA-BRUCEI APOCYTOCHROME-B MESSENGER-RNA HAVE AN UNUSUAL MINICIRCLE LOCATION AND ARE DEVELOPMENTALLY-REGULATED

We identified four different guide RNAs (gRNAs) that specify identical editing of Typanosoma brucei apocytochrome b (CYb) mRNA, which indica tes gRNA redundancy in T. brucei. All four gRNAs appear functional sin ce they occur in chimeras, some of which contain an interesting gRNA 3 ' ''extension.'' The gRNAs are encoded in different minicircles, rathe r than maxicircles as in other species. However, these gRNA genes are not between 18-base pair repeats as are the other minicircle gRNA gene s in T. brucei. The three minicircles cloned contain the same gRNA gen es, one of which is substantially diverged, all in the same order, ind icating that they are related. CYb gRNA is less abundant in procyclic than bloodstream forms. Procyclic forms contain abundant edited CYb mR NA unlike bloodstream forms thus suggesting that CYb mRNA editing may be regulated at the level of gRNA utilization.