Members of this strictly eukaryotic protein family are not RNA 3'-phosphate cyclase (6.5.1.4), but rather a homolog with a distinct function, found in the nucleolus and required for ribosomal RNA processing. Homo sapiens has both a member of this RCL (RNA terminal phosphate cyclase like) family and EC 6.5.1.4, while Saccharomyces has a member of this family only.