Structural gene expression of human immunodeficiency virus type 1 (HIV-1) requires a viral regulatory protein, Rev transactivator. We investigated Rev-dependency of HIV-1 gene expression by various reporter systems. Expression of unspliced and singly-spliced viral mRNAs was demonstrated to be differentially dependent on the Rev function. This difference of Rev-dependency was found not to be determined by cis-elements in gag, pol, and env coding sequences reported so far, and was lost when the reporter constructs containing minimum elements for Rev-responsiveness such as splice signals and rev responsive element were used for experiments. These findings indicated that fundamental structure of HIV-1 mRNA was critical for the differential regulation of gene expression by Rev transactivator.
