Document 0428 DOCN M9490428 TI A molecular rheostat. Co-operative rev binding to stem I of the rev-response element modulates human immunodeficiency virus type-1 late gene expression. DT 9411 AU Mann DA; Mikaelian I; Zemmel RW; Green SM; Lowe AD; Kimura T; Singh M; Butler PJ; Gait MJ; Karn J; MRC Laboratory of Molecular Biology, Cambridge, U.K. SO J Mol Biol. 1994 Aug 12;241(2):193-207. Unique Identifier : AIDSLINE MED/94334977 AB The complete biologically active human immunodeficiency virus type-1 (HIV-1) rev-response element (RRE) RNA is 351 nucleotides (nt) in length, and includes an extra 58 nt on the 5' end and 59 nt on the 3' end beyond the sites proposed in the original models for the RRE secondary structure. The extra sequences are able to form a duplex structure which extends Stem I. The presence of an elongated Stem I structure in the RRE RNA was confirmed by nuclease mapping experiments. Nuclease protection experiments have shown that rev binds to restricted regions of the RRE, including the high affinity site located at the base of Stem IIb and along the length of the Stem I region. The three large stem-loop structures which protrude from Stem I and Stem IIb (Stems IIc, III+IV and V) remain accessible to nucleases even in the presence of a large excess of protein. Gel-retardation experiments show that the truncations of Stem I reduced the total number of rev molecules that can bind co-operatively and with high affinity to the RRE RNA. To test whether the elongated Stem I structure is required for maximal rev activity, a series of truncations which progressively reduced the length of Stem I was introduced into an HIV-1 derived reporter plasmid. In the presence of rev and a functional RRE, there is an increase in the levels of gag and env mRNA in the cytoplasm and a decrease in levels of tat and rev mRNAs. Each of the truncations in Stem I reduced the rev responses, with the longest truncations producing the greatest losses of activity. The data suggest that the RRE acts as a molecular rheostat designed to detect rev levels during the early stages of the HIV growth cycle. DE Base Sequence Binding Sites Electrophoresis, Polyacrylamide Gel Gene Expression Regulation, Viral/*GENETICS Gene Products, rev/*METABOLISM Genes, env/*GENETICS Genes, gag/GENETICS Genes, tat/GENETICS Hela Cells Human HIV-1/*GENETICS Molecular Sequence Data Mutagenesis Nucleic Acid Conformation Polymerase Chain Reaction RNA, Viral/CHEMISTRY/*GENETICS/METABOLISM Support, Non-U.S. Gov't Transfection JOURNAL ARTICLE SOURCE: National Library of Medicine. NOTICE: This material may be protected by Copyright Law (Title 17, U.S.Code).