RNA editing associated with the generation of two distinct conformations of the trypanosomatid Leptomonas collosoma 7SL RNA

Analysis of the trypanosomatid Leptomonas collosoma 7SL RNA revealed the ex istence of two distinct stable 7SL RNA conformers (7SL I and II). Sequence analysis of the RNAs indicated a single base difference between the conform ers at position 133 (C in 7SL II and U in 7SL I) located in domain III, Thi s 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 positi on. 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, whe reas 7SL II is more abundant in ribosome-free particles. Mutations introduc ed in regions outside the editing site were found to occur in a single conf ormation, suggesting that the editing event is not the only factor that det ermines the conformation of the molecule. This study is the first descripti on of an editing event on a small RNA other than tRNA and is the first repo rt of C --> U editing in trypanosomes. We propose a novel role for RNA edit ing in controlling the conformation of the 7SL RNA in vivo.