ERVW-1 and AIDS: Early studies of HIV-1, the causative agent of acquired immunodeficiency syndrome (AIDS), revealed 3 classes of viral transcripts visible by northern blotting: (i) “full length” unspliced mRNA of about 9 kb; (ii) “intermediate” mRNAs of about 4 kb that included the singly-spliced env transcript; (iii) and “small” mRNAs of about 2 kb comprising several multiply spliced species [10].