FIG. 1.

Schematic representation of the proviral form of a retrovirus and its env gene products. (a) Genomic proviral structure and delineation of the TM subunit encoded by the env gene. The Mo-MuLV immunosuppressive domain (ISU) is shown, as is the degenerate CKS17d motif used for the initial screening of the databases (see text and Table 1; an extended optimized universal CKS17u motif [see Materials and Methods] which recognizes at least one member from each retroelement family of the CKS17-positive group in Fig. 3 and 5 was also devised). (b) Schematic structure of the env products, adapted from reference 17. CC, disulfide bond.