RESUMO
Analysis of the trypanosomatid Leptomonas collosoma 7SL RNA revealed the existence of two distinct stable 7SL RNA conformers (7SL I and II). Sequence analysis of the RNAs indicated a single base difference between the conformers at position 133 (C in 7SL II and U in 7SL I) located in domain III. This change appears to be the result of a post-transcriptional editing event, since the single-copy 7SL RNA gene codes exclusively for a C at this position. The edited form (7SL I) was found preferentially in the cytoplasm, and the pre-edited form in the nucleus. 7SL I is mainly bound to ribosomes, whereas 7SL II is more abundant in ribosome-free particles. Mutations introduced in regions outside the editing site were found to occur in a single conformation, suggesting that the editing event is not the only factor that determines the conformation of the molecule. This study is the first description of an editing event on a small RNA other than tRNA and is the first report of C --> U editing in trypanosomes. We propose a novel role for RNA editing in controlling the conformation of the 7SL RNA in vivo.
