Anti-termination by SIV Tat requires flexibility of the nascent TAR structure.
Substitution of the SIVmac239 promoter/enhancer by the strong EF1alpha promoter results in a severe replication defect due to a failure to respond to Tat. Revertant viruses with minimal promoter sequences (two Sp1 sites and a TATA box) were obtained that had fully restored their replicative potential. Comparison of the different LTRs indicated that structural alterations in the TAR stem due to a 31bp exon of the EF1alpha promoter rather than the mere presence of transcription factor binding sites within U3 were responsible for the attenuation. Structural models based on genuine RNA sequences combined with a refined algorithm to calculate the probability of the looping-mediated interaction between protein complexes bound to nucleic acid polymers indicated that the local concentration of TAR-bound Tat close to the RNA polymerase II complex was reduced more than 100-fold for the mutant as compared to SIVmac239. These results show that HIV/SIV replication requires only a minimal set of cis-acting elements in the promoter and suggest a hitherto unrecognised requirement of flexibility for the nascent TAR structure to allow anti-termination by Tat.
Sommer
Peter
P
Unité de Rétrovirologie Moléculaire, Pasteur Institute, 28 rue du Dr Roux, 75724 Paris, France. psommer@pasteur.fr
Vartanian
Jean-Pierre
JP
Wachsmuth
Malte
M
Henry
Michel
M
Guetard
Denise
D
Wain-Hobson
Simon
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D015870:Gene Expression; D015696:Gene Products, tat / Q000235:genetics* / Q000378:metabolism*; D006678:HIV / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D020648:Peptide Elongation Factor 1 / Q000235:genetics; D011401:Promoter Regions, Genetic; D012367:RNA, Viral / Q000737:chemistry / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D015302:Simian Immunodeficiency Virus / Q000235:genetics* / Q000378:metabolism*; D020079:Terminal Repeat Sequences; D015533:Transcriptional Activation; D014162:Transfection; D014779:Virus Replication / Q000235:genetics; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D020648:Peptide Elongation Factor 1; D012367:RNA, Viral; D054322:tat Gene Products, Human Immunodeficiency Virus