Schematic representation of gag mRNAs and their translation phenotypes. Full length viral mRNA is capped (7MeG) and polyadenylated (An), as are all other constructs. At the 5' and 3' ends of the viral genome length RNA, the R and U5 or U3 elements are indicated as grey (R) blue (U5) and purple boxes (U3). The viral open reading frames (ORF) gag, pol, and env are indicated while other genes are not presented to maintain clarity. The splice donors (SD) and splice acceptors (SA) are represented as green or orange triangles, respectively. The viral protein Rem (blue half moon) is shown bound to its cis RNA structural element, the RmRE. Three subviral mRNAs, derived from various CMV promoter constructs, are also depicted. The minimal expression construct contains only the cap, gag ORF, and poly-A tail. Also depicted is the mRNA from a gag bicistronic construct that contains an IRES element supporting cap-independent translation of eGFP. The second subviral construct includes the RmRE, to which Rem (provided in trans) is shown to bind. The third subviral gag expression construct contains both a SD and SA positioning the gag ORF in an intron as well as the RmRE and Rem in trans. Expression of Gag protein from the different mRNAs is indicated as a purple polypeptide exiting the ribosome (red). For subviral constructs, loss of protein expression as a result of the included gag allele is indicated by dotted lines and by the absence of Gag polypeptide exiting the ribosome. Similarly, when the bicistronic constructs fail to support Gag expression, the lack of GFP production from the IRES is indicated by the dotted line and lack of the green polypeptide exiting the ribosome. The lightning bolt represents direct transfection of gag mRNAs where allele-independent Gag translation was detected.