New antiviral strategy using capsid-nuclease fusion proteins

Overexpression of dominant-negative mutants of various viral proteins can result in 'intracellular immunization' (refs 1, 2). Here we describe a new approach to interfering with viral replication in which a nuclease is fused to a capsid component so that the nuclease is encapsidated inside the virion where it can inactivate viral nucleic acid. We used Tyl, a yeast retrotransposon whose transposition closely parallels retroviral replication mechanisms and serves as an easily manipulated model for the retroviral infection process³. We constructed fusion genes consisting of the region encoding the N-terminal portion of the TYA/TYB open reading frames of retrotransposon Tyl and either of two different nuclease genes. Tyl-nuclease fusion proteins are targeted to Tyl virus-like particles, and are active in degrading nucleic acids. A Tyl-barnase fusion protein causes 98-99% reduction in the efficiency of Tyl transposition in vivo, presumably by degrading encapsidated Tyl RNA. This strategy, referred to as capsid- targeted viral inactivation, may be useful for interfering with the replication of retroviruses and other viruses.