Gene inactivation by frameshift mutation provides rapid adaptation of an attenuated vaccinia virus

The work describes experimental evolution studies using hybrid attenuated vaccinia virus with the gene encoding intermediate transcription factor replaced by orthologous gene from myxoma virus.The increase in fitness of attenuated virus in the course of 10 passages was achieved due to the inactivation of some nonessential genes but not by the modification of transcription apparatus genes as expected. Thus, in poxvirus evolution gene inactivation, in addition to gene duplication and base substitution, has the potential of enhancing virus replication.