The present invention relates to nucleic acids encoding SID polypeptides which bind selectively to a polypeptide encoded by a pathogenic strain of the hepatitis C virus, as well as to the SID polypeptides which are encoded by said nucleic acids. The invention also concerns vectors comprising a nucleic acid encoding a SID polypeptide as well as host cells transformed with such vectors. The invention is also directed to two-hybrid methods which make use of the nucleic acids encoding a SID polypeptide selected from a pathogenic strain of the hepatitis C virus as well as to methods for selecting molecules which inhibit the binding between a SID polypeptide and a polypeptide which specifically binds thereto.