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 C. elegans , and exclusively at the ced-2 /CRKII- set-23 /SETMAR operon. Comparative analysis across nematodes, including C. briggsae , C. brenneri , and distantly related B. malayi , shows that these repeats are conserved at all ced-2 /CRKII- set-23 /SETMAR loci. Furthermore, between C. elegans and B. malayi 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.