<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>The genes coding for the Regulator X (rex) protein of HTLV-I and II. The Rex phosphoprotein binds to a cis-acting Rex response element in the RNA transcript. It is required for the nuclear export of unspliced viral RNA, and therefore essential for packaging of the RNA in virions.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>