A 300 bp non-coding repeat sequence has co-evolved with the ced-2/CRKII-set-23/SETMAR genes of nematodes

Highly conserved non-coding repeats may encode sequences with regulatory functions. We report a ~300 nucleotide non-coding repeat found four times in <i>C. elegans ,</i> and exclusively at the <i>ced-2 /CRKII- set-23 /SETMAR</i> operon. Comparative analysis across nematodes, including <i>C. briggsae , C. brenneri</i> , and distantly related <i>B. malayi</i> , shows that these repeats are conserved at all <i>ced-2 /CRKII- set-23 /SETMAR</i> loci. Furthermore, between <i>C. elegans</i> and <i>B. malayi</i> these repeats are more highly conserved than the CED-2 /CRKII coding sequences. These findings suggest the repeats are conserved regulatory modules coordinating CED-2 and SET-23 expression. Supporting this idea, the repeats partially resemble miRNA precursors.