INHIBITORY ACTIVITY OF THE EQUINE INFECTIOUS-ANEMIA VIRUS MAJOR 5'-SPLICE-SITE IN THE ABSENCE OF REV

The major 5' splice site of equine infectious anemia virus (EIAV) conf orms to the consensus 5' splice site in eight consecutive positions an d is located immediately upstream of the gag AUG. Our results show tha t the presence of this 5' splice site on the EIAV gag mRNA decreases G ag production 30- to 60-fold. This is caused by inefficient nuclear mR NA export and inefficient mRNA utilization. Inhibition could be overco me by providing human immunodeficiency virus type 1 Rev/Rev-responsive element, human T-cell leukemia virus type 1 Rex/Rex-responsive elemen t, or simian retrovirus type 1 constitutive transport element. In addi tion, inhibition could be abolished by introducing single point mutati ons in the 5' splice site or by moving the 5' splice site away from it s natural position immediately upstream of the gag AUG. This demonstra tes that both maintenance of a perfect consensus 5' splice site and it s proper location on the mRNA are important for inhibitory activity of the EIAV major 5' splice site.