Phosphorescence and optically detected magnetic resonance investigation of the binding of the nucleocapsid protein of the human immunodeficiency virus type 1 and related peptides to RNA.

The RNA and DNA complexes of nucleocapsid protein p7.Zn (NCp7.Zn) of the human immunodeficiency virus type 1 (HIV-1) are studied by phosphorescence and optically detected magnetic resonance (ODMR). The single tryptophan, Trp37, which is located on the C-terminal zinc finger domain is used as an intrinsic probe. Reductions in the triplet state zero-field splitting (zfs) D parameter of Trp37 upon complex formation with poly(I) and poly(U) are observed. These results, in conjunction with the phosphorescence red-shifts and triplet state lifetime reductions that are observed, suggest the presence of aromatic stacking interactions between NCp7.Zn and the bases of the RNA polymers. An alteration of the intersystem crossing pattern upon complex formation, in addition to the above mentioned spectroscopic shifts, also is consistent with previously observed tryptophans that undergo stacking interactions with DNA bases [Zang, L.-H., Maki, A.H., Murphy, J.B., & Chase, J.W. (1987) Biophys. J. 52, 867-872. Tsao, D.H.H., Casas-Finet, J.R., Maki, A.H., & Chase, J.W. (1989) Biophys. J. 55, 927-936]. These conclusions support those from a recent ODMR study [Lam, W.-C., Maki, A.H., Casas-Finet, J.R., Erickson, J.W., Sowder, R.C., II, & Henderson, L.E. (1993) FEBS Lett. 328, 45-48] of NCp7.Zn binding to 5-mercurated polyuridylic acid [poly(5-HgU)] in which stacking interactions between the RNA and NCp7.Zn are inferred from the observation of an external heavy atom effect induced on Trp37.(ABSTRACT TRUNCATED AT 250 WORDS)