Figure 1. Potential secondary structures for Y RNAs. (A) The four human Y RNAs. A conserved helix present in all animal cell Y RNAs is boxed. Nucleotides within this helix are important for Ro60 binding.13–15 The proposed structures are consistent with phylogenetic analyses52 and enzymatic probing experiments.11,53 (B) X. laevis Y3 RNA. Structural and enzymatic probing studies show that nucleotides in the conserved helix can form two alternate conformers.14,15,53 Sequences present in the X. laevis Ro60/Y3 RNA crystal structure are in bold type. (C) D. radiodurans Y RNA. Regions involved in Rsr and PNPase binding are shown.30