NO TRNA(3)(LYS) UNWINDING IN A COMPLEX WITH HIV NCP7

The nucleocapsid protein NCp7 of the human immunodeficiency virus (HIV ) type 1 is important for the annealing of HIV RNA and tRNA(3)(Lys), t he tRNA acting as a primer during reverse transcription of HIV RNA, A wild type NCp7 and a Cys(23) mutant having a disrupted zinc finger wer e analyzed with far UV circular dichroism (CD), CD data analysis revea led that NCp7 has a high content of extended structures in aqueous buf fer, decreasing in Cys(23) NCp7 and in NCp7 in the absence of zinc, An increase in beta-turn structures is observed in NCp7 bound to tRNA(3) (Lys). Furthermore, CD data shows that Cys(23) NCp7 binds tRNA(3)(Lys) . The CD spectrum of tRNA(3)(Lys) is typical of an A-form helix and re tains this structure after binding of NCp7, which demonstrates that NC p7 does not induce tRNA(3)(Lys) unwinding, CD spectra of tRNA(3)(Lys) were measured from 5 to 80 degrees C to observe CD changes resulting f rom tRNA(3)(Lys) melting. Molecular modeling of the complex identifies two potential tRNA anticodon binding sites in the NCp7 N-terminal reg ion and first zinc finger, In this model, both binding sites can inter act with 12 nucleotides in the anticodon domain without requiring a ba se specificity.