Structure of plasmids used to determine RNA export activity. The CMV promoter (gray box) is shown inserted upstream of the 3' end of the MMTV provirus (solid horizontal line). The 3' MMTV LTR is shown by a white box. The Renilla luciferase gene (black box) is located between the splice donor (SD) and acceptor (SA) sites. The smaller hatched box indicates the SV40 polyadenylation region. The smaller gray box shows the position for insertion of response elements for other retroviral export proteins within the HMΔeLTRluc plasmid.