Complex sentence: Some species contain only one spliced leader sequence which is found on all mRNA's, in C. elegans two are seen labeled SL1 and SL2 (Huang and Hirsh 1989).
Split into simpler sentences: Some species contain only one spliced leader sequence found on all mRNAs. In C. elegans two are seen and are labeled SL1 and SL2 (Huang and Hirsh 1989).