The Qβ gene C has been proposed as a new carrier for the exposure of foreign peptide sequences. Contrary to well-known ‘display vectors’ on the basis of coat proteins of RNA phage group I, group III phage Qβ-based vectors suggested application of the 195-amino acid extension of coat protein (CP) within the so-called Al protein for insertion of the appropriate immunological epitopes. ‘Mosaic’ capsids presenting model hepatitis B virus preSl and HIV-1 gpl20 epitopes and formed by Qβ CP together with A1-derived proteins were obtained as a result of (1) suppression of leaky UGA stop codon of the CP gene and (2) simultaneous expression of’pure’ CP and full-length A1-derived genes obtained after the changing of CP-terminating UGA to strong UAA stop codon or sense GGA codon