FIG. 1.

Candidate DIS loci in the Mo-MuLV genome. (A) Schematic depiction of the Mo-MuLV 5′ leader region, extending from the first transcribed base (residue 1) in the R region through the gag start codon (to residue 621). Locations of the primer binding site (PBS), major 5′ splice donor (SD), and palindromic portions of four putative stem-loop structures are shown. Of the latter, DIS-1 and DIS-2 are considered in this study; the two downstream stem-loops appear to serve as the core RNA packaging signal (ψ) (see reference 35). (B) Hypothetical pathways of kissing-loop dimerization for DIS-1 and DIS-2. Each initially homodimerizes through four central palindromic bases in and around its loop, forming a transient kissing-loop complex which then can isomerize into linear form.