Document 0285
 DOCN  M94A0285
 TI    Nucleic acid binding properties of recombinant Zn2 HIV-1 nucleocapsid
       protein are modulated by COOH-terminal processing.
 DT    9412
 AU    Khan R; Giedroc DP; Department of Biochemistry and Biophysics, Texas A&M
       University,; College Station 77843-2128.
 SO    J Biol Chem. 1994 Sep 9;269(36):22538-46. Unique Identifier : AIDSLINE
       MED/94357893
 AB    The nucleocapsid protein (NC) of all animal retroviruses is the major
       structural protein of the core ribonucleoprotein complex, bound to
       genomic RNA in mature virions. In a previous report, we showed that
       recombinant NC protein from HIV-1, a 71-amino-acid protein (NC71), is
       apparently able to form two types of protein-nucleic acid complexes
       under low [NaCl], pH 8.3 and 25 degrees C. These appeared to differ in
       occluded apparent site size, napp, forming n = 8 and n = 14 complexes on
       poly(A) (Dib-Hajj, F., Khan, R., and Giedroc, D. P. (1993) Protein Sci.
       2, 331-243) under conditions of high and low protein-nucleotide ratios,
       respectively. Here we show that both NC71-poly(A) complexes strongly
       scatter light under these solution conditions. Examination of the
       wavelength dependence of the light scattering at lambda < or = 320 nm
       indicates that each complex is characterized by a different scattering
       coefficient. Optical density measurements suggest that upon formation of
       the saturated n = 8 complex, additional polynucleotide is not
       incorporated into the complex over a period of hours, i.e. the n = 14
       complex is not formed via redistribution of the n = 8 complex under low
       salt conditions, 25 degrees C. In contrast, the n = 14 complex readily
       incorporates additional protein until that sufficient to form the n = 8
       complex is present. The n = 14 complex efficiently precipitates poly(A)
       and shows spectral characteristics expected for an extensively
       charge-neutralized nucleic acid complex. At [NC71] in excess of that
       required to form the n = 8 complex, this n = 14 complex is best
       described as a kinetic intermediate on the pathway to the n = 8 complex,
       which forms over a period of hours under low salt conditions, 25 degrees
       C. This slow kinetics of binding provides a possible explanation for the
       finding that the previously observed moderate cooperativity of Zn2 NC71
       binding to poly(A) (omega = 200) at pH 8.3 and 0.29 M NaCl (Khan, R.,
       and Giedroc, D. P. (1992) J. Biol. Chem. 267, 6689-6695) is shown here
       to represent a nonequilibrium phenomenon, apparently converting to a low
       or no cooperativity complex over a period of hours. Proteolytic removal
       of the COOH-terminal 14 amino acids from NC71, forming a 57-amino-acid
       protein (denoted NC57), removes this apparent binding site size
       heterogeneity of NC71 on poly(A). At 20 mM NaCl, NC57 binds with n = 6-7
       nucleotides, in a manner which is independent of the protein-poly(A)
       nucleotide ratio. The implications of these findings on processing of
       the gag precursor which leads to mature NC in HIV-1 virions is
       discussed.
 DE    Amino Acid Sequence  Capsid/*METABOLISM  Circular Dichroism  Comparative
       Study  Gene Products, gag/BIOSYNTHESIS/CHEMISTRY/*METABOLISM
       HIV-1/*METABOLISM  Kinetics  Molecular Sequence Data  Poly A/*METABOLISM
       Protein Binding  Protein Conformation  Recombinant
       Proteins/BIOSYNTHESIS/CHEMISTRY/*METABOLISM  RNA-Binding
       Proteins/BIOSYNTHESIS/CHEMISTRY/*METABOLISM  Spectrometry, Fluorescence
       Support, Non-U.S. Gov't  Support, U.S. Gov't, P.H.S.  Virion/METABOLISM
       JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).