HIV-1 Tat protein interacts with mammalian capping enzyme and stimulates capping of TAR RNA.
HIV gene expression is subject to a transcriptional checkpoint, whereby negative transcription elongation factors induce an elongation block that is overcome by HIV Tat protein in conjunction with P-TEFb. P-TEFb is a cyclin-dependent kinase that catalyzes Tat-dependent phosphorylation of Ser-5 of the Pol II C-terminal domain (CTD). Ser-5 phosphorylation confers on the CTD the ability to recruit the mammalian mRNA capping enzyme (Mce1) and stimulate its guanylyltransferase activity. Here we show that Tat spearheads a second and novel pathway of capping enzyme recruitment and activation via a direct physical interaction between the C-terminal domain of Tat and Mce1. Tat stimulates the guanylyltransferase and triphosphatase activities of Mce1 and thereby enhances the otherwise low efficiency of cap formation on a TAR stem-loop RNA. Our findings suggest that multiple mechanisms exist for coupling transcription elongation and mRNA processing.
Department of Pharmacology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
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Chiu
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Coronel
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Shuman
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D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015696:Gene Products, tat / Q000737:chemistry / Q000378:metabolism*; D016325:HIV Long Terminal Repeat / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008322:Mammals; D051379:Mice; D009690:Nucleic Acid Conformation; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine; D012319:RNA Polymerase II / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D054322:tat Gene Products, Human Immunodeficiency Virus; D000098556:mRNA Guanylyltransferases
D015696:Gene Products, tat; D011994:Recombinant Proteins; D054322:tat Gene Products, Human Immunodeficiency Virus; D010768:Phosphoserine; D009713:Nucleotidyltransferases; D012319:RNA Polymerase II; C020842:guanylyltransferase; D000098556:mRNA Guanylyltransferases; D012260:Ribonucleases