Putative nucleotidyltransferase required for several aspects of embryonic development including normal development of the eye (By similarity). It is unclear whether it displays nucleotidyltransferase activity in vivo. Binds single-stranded RNA (ssRNA) (By similarity). Monomer. Homodecamer; composed of 2 back to back homopentamers. The protein may exist as monomer in solution and oiligomerizes upon ligand binding. Belongs to the mab-21 family.