A smaller terminal loop was revealed in the KFDV/ AHFV and KSIV sequences resulting in the formation of the tetraloop U(GCCA)A ( Figure 1B ). The presence of U:A as a loop-closing base pair has been shown to decrease tetraloop stability considerably; in combination with some intraloop sequences this results in intermolecular tensions that prevent the folded tetraloop from achieving a global thermodynamic minimum (38, 39) . Thus, despite the MFold-mediated predictions, a tetraloop may not form for KFDV/AHFV and KSIV or at least not be sufficiently stable for biologically significant (RNA-RNA or RNA-protein) interactions.