This family of eukaryotic proteins includes Saccharomyces cerevisiae Ydl063c and Chaetomium thermophilum Syo1, which mediate the co-import of two ribosomal proteins, Rpl5 and Rpl11 (which both interact with 5S rRNA) into the nucleus. Import precedes their association with rRNA and subsequent ribosome assembly in the nucleolus. The primary structure of syo1 is a mixture of Armadillo- (ARM, N-terminal part of syo1) and HEAT-repeats (C-terminal part of syo1).