THE S2 GENE OF EQUINE INFECTIOUS-ANEMIA VIRUS IS DISPENSABLE FOR VIRAL REPLICATION IN-VITRO

Equine infectious anemia virus (EIAV) contains the simplest genome amo ng lentiviruses in that it encodes only three putative regulatory gene s (SI, S2, S3) in addition to the canonical gag, pal, and env genes, p resumably reflecting its limited tropism to cells of monocyte/macropha ge lineage. Tat and Rev functions have been assigned to SI and S3, res pectively, but the specific function for the S2 gene has yet to be det ermined. Thus, the function of S2 in virus replication in vitro was in vestigated by using an infectious molecular viral clone, EIAV,, Variou s EIAV,, mutants lacking S2 were constructed, and their replication ki netics were examined in several equine cell culture systems, including the natural in vivo target equine macrophage cells. The EIAV S2 mutan ts showed replication kinetics similar to those of the parental virus in all of the tested primary and transformed equine cell cultures, wit hout any detectable reversion of mutant genomes. The EIAV,, mutants al so showed replication kinetics similar to those of the parental virus in an equine blood monocyte differentiation-maturation system. These r esults demonstrate for the first time that the EIAV S2 gene is not ess ential and does not appear to affect virus infection and replication p roperties in target cells in vitro.