Identification of the first trypanosome H/ACA RNA that guides pseudouridine formation on rRNA

In trypanosomes small nucleolar RNA (snoRNA) genes are clustered, and the c lusters encode for either single or multiple RNAs. We previously reported o n a genomic locus in Leptomonas collosoma that encodes for multiple C/D sno RNAs whose expression is regulated at the processing level (Xu, Y., Liu, L. , Lopez-Estrano, C., and Michaeli, S. (2001) J. Biol. Chem. 276, 14289-1429 8). In this study we have characterized, in the same genomic locus, the fir st trypanosome H/ACA RNA, which we termed hl. Having a length of 69 nucleot ides, hl has the potential to guide pseudouridylation on 28 S rRNA. The hl is processed from a long polycistronic transcript that carries both the C/D and hl snoRNAs. The h1/rRNA duplex obeys the rules for guiding pseudouridy lation. Mapping of the pseudouridine site indicated that the predicted U is indeed modified. However, in contrast to all H/ACA RNAs, hl consists of a single hairpin structure and is the shortest H/ACA RNA described so far.