FIG. 1.

JSRV Env constructs and their transforming activities. Shown at the top is the JSRV Env protein which is processed into the SU and TM subunits of the mature Env as indicated. The presumed endoplasmic reticulum signal peptide (SP), membrane-spanning domain (M), and cytoplasmic tail (CT) are shown. In FLAG-Jenv, the first 72 amino acid residues of JSRV Env were replaced by the signal sequence of preprotrypsin followed by a FLAG sequence (SS-FLAG). A similar construct was also created for ENTV Env, FLAG-Eenv (not shown). Jenv-FLAG is identical to the wild-type Env, except that a FLAG sequence was attached to its cytoplasmic tail. JSRV-MLV and JSRV-HIV-1 are two chimeras in which the cytoplasmic tails of JSRV Env were replaced with those of 10A1-MLV and HIV-1, respectively. JSU-hIgG was designed to express JSRV SU-human IgG Fc fusion protein as described previously (19). Shown at right are the transforming activities of each construct measured using the 2-week transformation assay.