A method for designing a protein capable of binding in an RNA base selective manner or RNA base sequence specific manner is provided. The protein of the present invention is a protein containing one or more of PPR motifs (preferably 2 to 14 PPR motifs) each consisting of a polypeptide of 30- to 38-amino acid length represented by the formula 1 (wherein Helix A is a moiety of 12-amino acid length capable of forming an ±-helix structure, and is represented by the formula 2, wherein, in the formula 2, A 1 to A 12 independently represent an amino acid X does not exist, or is a moiety of 1- to 9-amino acid length Helix B is a moiety of 11- to 13-amino acid length capable of forming an ±-helix structure and L is a moiety of 2- to 7-amino acid length represented by the formula 3, wherein, in the formula 3, the amino acids are numbered "i" (-1), "ii" (-2), and so on from the C-terminus side, provided that L iii to L vii may not exist), and combination of three amino acids A 1 , A 4 and L ii , or combination of two amino acids A 4 , and L ii is a combination corresponding to a target RNA base or base sequence.
