SPLICED LEADER-ASSOCIATED RNA OF TRYPANOSOMES - SEQUENCE CONSERVATIONAND ASSOCIATION WITH PROTEIN-COMPONENTS COMMON TO TRANS-SPLICEOSOMAL RIBONUCLEOPROTEINS

A spliced leader-associated (SLA) RNA recently identified in Trypanoso ma brucei has been proposed as a U5 RNA analog in trans-splicing, base d on in vivo psoralen cross-linking to the spliced leader (SL) RNA and a short stretch of homology to a conserved U5 RNA sequence. Here we s how that the SLA RNA is in the form of an RNP containing common protei ns that also occur in the known trans-spliceosomal snRNPs of T. brucei , the SL, U2, and U4/U6 snRNPs. Therefore the SLA RNP is a member of a larger family of related RNPs. The immunoprecipitation of the SLA RNA by antibodies against common proteins does not require an association between the SLA RNA and the SL RNP. To identify sequences of potentia l functional importance and to establish a secondary structure model, we have sequenced the SLA RNA and cloned its gene from a related trypa nosomatid, Leptomonas seymouri. A sequence comparison between the T. b rucei and L. seymouri SLA RNAs reveals that the U5-homologous sequence element is not conserved.