Maturation of most eukaryotic mRNAs involves RNA splcing. Therefore, understanding of mechanism of RNA splcing is central to understanding gene expression. Maturation of some mRNAs in C. elegans (involves the acquisition of one of two spliced leaders through tran-splcing. The two spliced leaders are specifically trans-spliced to different mRNAs and the reaction is very specific. Therefore, understanding the mechanism of trans-splicing is central to understanding gene expression in C. elegans. The working hypothesis of this proposal can be stated as follows: There are different classes of trans-spliceosomes in C. elegans with the difference being the presence of SL1 snRNP or SL2 snRNP. In addition, trans-splicing and cis-splicing in C. elegans occur on separate classes of spliceosomes. The difference between these classes is the presence of SL snRNP in trans-spliceosomes and U1 snRNP in cis-spliceosomes. Other snRNPs are common to both classes of spliceosomes. Using a molecular genetic approach, the PI will investigate two key questions concerning the mechanism of RNA splicing in C. elegans. What nucleotides of SL RNAs are important in determing specificity during trans-splicing and is trans-splicing independent of U1 of snRNP?