DIRECT INTERACTIONS BETWEEN AUTOANTIGEN LA AND HUMAN-IMMUNODEFICIENCY-VIRUS LEADER RNA

We have characterized the in vivo and in vitro binding of human La protein to the human immunodeficiency virus type 1 (HIV-1) leader RNA, the trans-activation response element (TAR). In immunoprecipitation studies using anti-La serum, La-TAR ribonucleoprotein; were recovered from HIV-1-infected lymphocytes. Further characterization of this interation revealed that La has preference for the TAR stem. However, TAR RNA recognition tolerated changes in the primary sequence of the stem as long as the secondary; structure was conserved. This structural aspect-of La-TAR recognition was confirmed in competition studies in which certain homopolymers influenced complex formation while other single-stranded and double-stranded RNAs had no effect. Deletion mutants of recombinant La protein were used to demonstrate that the residues responsible for binding to polymerase III precursor transcripts overlapped the binding domain for the TAR leader RNA. This finding;ling of a direct interaction between La and TAR has functional implications for translational regulation of HIV-1 mRNAs as demonstrate in the accompanying report (Y. V. Svitkin, A. Pause, and N. Sonenberg, J. Virol. 68:7001-7007, 1994).