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

We have characterized the in vivo and in vitro binding of human La pro tein to the human immunodeficiency virus type 1 (HIV-1) leader RNA, th e trans-activation response element (TAR). In immunoprecipitation stud ies using anti-La serum, La-TAR ribonucleoprotein; were recovered from HIV-1-infected lymphocytes. Further characterization of this interati on revealed that La has preference for the TAR stem. However, TAR RNA recognition tolerated changes in the primary sequence of the stem as l ong as the secondary; structure was conserved. This structural aspect- of La-TAR recognition was confirmed in competition studies in which ce rtain homopolymers influenced complex formation while other single-str anded and double-stranded RNAs had no effect. Deletion mutants of reco mbinant La protein were used to demonstrate that the residues responsi ble 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 transla tional regulation of HIV-1 mRNAs as demonstrate in the accompanying re port (Y. V. Svitkin, A. Pause, and N. Sonenberg, J. Virol. 68:7001-700 7, 1994).