A Chimeric Human Immunodeficiency Virus Type 1 TAR Region Which Mediates High Level Trans-activation in Both Rodent and Human Cells

Abstract

Trans-activation of the HIV-1 LTR by the Tat protein functions by a novel mechanism which involves the direct interaction of the Tat protein and cellular factors with nascently transcribed viral RNA encoding the Tat responsive element (TAR). Rodent cells do not efficiently support HIV-1 Tat activity because of a deficiency of human-specific factor(s). Human chromosome 12 appears to encode one of these Tat cofactors. We have designed chimeric TAR sequences which contain the heterologous RNA sequence derived from the bacteriophage R17 genome which binds to the bacteriophage MS2 coat protein. These chimeric TAR constructs were co-transfected into rodent and human cells with a plasmid encoding a chimeric Tat protein which contains the RNA binding domain of the MS2 coat protein. TAR constructs which contain the MS2 coat protein binding region inserted into the three nucleotide "bulge" region support a high level of trans-activation by Tat-MS2 coat protein chimeras in both human and rodent cells. This result suggests that the human-specific Tat cofactor(s) may act to allow Tat to interact effectively in a ribonucleoprotein complex which includes Tat, cellular factors, and TAR RNA.