[
International C. elegans Meeting,
2001]
Nematodes represent an extremely diverse phylum with five major clades containing both free living and parasitic representatives (Blaxter et. al. 1998). The genome of the clade V nematode Caenorhabditis elegans contains many gene clusters which are transcribed as polycistronic pre-messenger RNAs. Unfortunately there is currently no information on the genomic organization of any nematodes other than the free living rhabditids Oscheius brevesophaga, C. elegans and C.briggsae (Evans et. al. 1997). One particularly interesting question is whether these operon-like structures are conserved in other nematode species and if they are do they utilize SL2-like spliced leaders to resolve the polycistronic transcripts. We have employed a directed approach using ribosomal protein operons found in the C. elegans genome and the Nematode EST datasets (Parkinson et. al. 2001) to identify a potential operon in a selection of clade V, IV, and III nematodes. In the clade III filarial nematode Brugia malayi we have determined that the rpL27a and rpP1 are transcribed as a polycistronic unit. However, the second transcript in the unit (rpP1) exclusively receives SL1 when it is transpliced. Conversely in the clade V diplogasterid Pristionchus pacificus we have found that a diverse set of SL2-like sequences transpliced to rpP1. In a survey of the genome sequence of C. elegans we identified several additional SL2-like sequences that had not been previously described. This data indicates that while SL2 usage may have evolved in a clade V ancestor, there have been independent expansions of SL2-like sequences in the rhabditids and diplogasterid. We are currently examining the rpP1 of the clade IV nematode Strongyloides ratti to determine if it utilizes SL2-like spliced leaders.