FIG. 1.

Structure of SIN HIV-derived vectors. A schematic representation of an HIV-1 vector with enlarged 3′ LTR to show the binding sites for differents transcription factors on U3 is shown (not to scale). Although the 3′ LTR is depicted, the nucleotide numbering refers to the cap site at the beginning of R as +1 as for a 5′ LTR. Position −418 is the 5′ limit of all deletions; positions −78, −45, −36, and −18 indicate the 3′ limits of the different deletions described in the text. The deletion generating the SIN-18 vector created a novel BglII site. Details on the nuclear factors binding U3 can be found in references 10, 15, and 22 and references therein. SD, splice donor; RRE, Rev-response element; SA, splice acceptor. The GenBank accession number for the wild-type 3′ LTR is M1991.