This domain is found in three copies in the N-terminus of the C. elegans RSD-2 protein. RSD-2 (RNAi spreading defective) is involved in systemic RNAi [1]. Mutations in the rsd-2 gene do not effect somatic genes but only germline expressed genes [1].

1: Genes Required for Systemic RNA Interference in Caenorhabditis elegans. Tijsterman M, May RC, Simmer F, Okihara KL, Plasterk RH; Curr Biol 2004;14:111-116. PMID:14738731