The U6 snRNA-encoding gene of the monogenetic trypanosomatid Leptomonas collosomat

Abstract

The U6 snRNA (U6) is the most conserved small nuclear RNA (snRNA) and apparently plays a central role in catalysis of the cis-splicing reaction. In trans-splicing, U6 may have an additional function. In the nematode trans-splicing system, a direct interaction between the U6 and spliced leader (SL) RNAs has been demonstrated, suggesting that U6 may serve as a bridge between the SL RNA and the acceptor pre-mRNA. To examine possible phylogenetic conservation of trypanosomatid U6 sequences that may interact with spliceosomal RNAs, we have cloned and sequenced the U6 gene from the monogenetic trypanosomatid Leptomonas collosoma ( Lc). The Lc U6 deviates from the Trypanosoma brucei ( Tb) RNA only in four positions located in the 5′ stem-loop and the central domains. As in Tb, U6 is a single-copy gene and two tRNA genes, tRNA Gln and tRNA Ile, are found upstream to the gene. The tRNAs are differentially expressed; tRNA Gln is transcribed in the opposite direction to U6, whereas tRNA Ile is not transcribed. Possible base-pairing between U6 and the U2 and SL RNAs, similar to the interactions that take place in the nematode trans-splicing system, are proposed.