The genes for small nucleolar RNAs in Trypanosoma brucei are organized in clusters and are transcribed as a polycistronic RNA

Because the organization of snoRNA genes in vertebrates, plants and yeast i s diverse, we investigated the organization of snoRNA genes in a distantly related organism, Trypanosoma brucei. We have characterized the second exam ple of a snoRNA gene cluster that is tandemly repeated in the T.brucei geno me, The genes encoding the box C/D snoRNAs TBR12, TBR6, TBR4 and TBR2 make up the cluster, In a genomic organization unique to trypanosomes, there are at least four clusters of these four snoRNA genes tandemly repeated in the T. brucei genome. We show for the first time that the genes encoding snoRN As in both this cluster and the SLA cluster are transcribed in an unusual w ay as a polycistronic RNA.