Abstract: The invention relates to a nucleic acid sequence, called “polyribozyme”, which has an endoribonuclease activity and is capable of inactivating the gene for the capsid protein of a virus, characterized in that it comprises: i) a sequence complementary to at least a part of the gene or its transcript or to its replication intermediates and, includes at distinct sites in this complementary sequence: ii) a plurality of ribozyme catalytic regions; iii) and, optionally, one or more sequences non-complementary to the transcript of the said gene, the said non-complementary sequence(s) being inserted between two consecutive bases of the complementary sequence.