All lentiviruses have in their genomes a tat gene which encodes a short protein called Tat. Primate lentivirus HIV (Human Immunodeficiency Virus) and SIV (Simian Immunodeficiency Virus) Tat proteins play a crucial role in transactivation of their silent LTRs. In contrast, the called Tat protein of Small Ruminant Lentiviruses (SRLVs) was found to have no prominent role in transactivation of their LTR promoters. In our recent works we demonstrated that this called Tat protein is rather an accessory Vpr-like than a regulatory Tat protein. The absence of this regulatory and the presence of an accessory protein will be discussed.