The dependence of Rev-mediated nuclear export of EIAV mRNA on Rev multimerization is modulated by mRNA length

All lentiviruses encode a regulatory protein, Rev, which mediates nuclear export of viral mRNAs and is required for viral replication, and multimerization of Rev is thought to be critical for its function. The lentivirus equine infectious anemia virus (EIAV) Rev is known to mediate the nuclear export of long-length, unspliced, or incompletely spliced viral mRNA encoding the viral structural proteins (Gag, Pol, and Env), like Rev from other lentiviruses. However, EIAV Rev also mediates the nuclear export of a short-length, fully spliced viral mRNA species encoding the functionally unknown protein Mat. Here, we found that disruption of Rev multimerization impaired Rev activity in mediating nuclear export and expression of gag-pol mRNA, but not in mediating nuclear export and expression of mat mRNA. Deficiency of Rev multimerization leads to lower viral replication. Further investigation revealed that the activity of multimerization-deficient Revs in mediating nuclear export and expression of long-length EIAV or HIV-1 mRNAs was significantly lower than that of wild-type Rev, while this difference was significantly reduced or absent between the two in mediating nuclear export and expression of short-length EIAV or HIV-1 mRNAs. This suggests that the differential dependence of the nuclear export of gag-pol mRNA and mat mRNA on Rev multimerization is modulated by the lengths of the mRNA species. Our findings suggest that when targeting short mRNAs, EIAV Rev appears to be able to perform nuclear export activity in a non-multimerized state.IMPORTANCEMultimerization of lentiviral Rev is thought to be essential for its function, which is to mediate nuclear export of viral mRNA, a necessary step in lentiviral replication. In equine infectious anemia virus (EIAV), the nuclear export of unspliced viral mRNAs encoding structural proteins (Gag/Pol) is dependent on Rev. Moreover, our recent studies have demonstrated that the nuclear export of a fully spliced mRNA species, mat, encoding a small protein (Mat) of unknown function, is also Rev-dependent. In this study, we observed that the expression and nuclear export of EIAV gag-pol mRNA were strictly dependent on Rev multimerization, whereas those of mat mRNA were not. Interestingly, we also determined that the dependence of Rev-mediated nuclear export of EIAV mRNA on Rev multimerization is strongly associated with lengths of these mRNA species. Our data imply that EIAV Rev is able to exert nuclear export activity in a non-multimerized state.