d'Adda di Fagagna F, Marzio G, Gutierrez MI, Pedacchia D, Falaschi A, Giacca M; International Conference on AIDS.
Int Conf AIDS. 1993 Jun 6-11; 9: 147 (abstract no. PO-A05-0077).
International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
The 5' LTR of HIV-1 is an interdigitated array of binding sites for human transcription factors which regulate viral transcription initiation. We have previously demonstrated that the dyad symmetry motif CACPuTG motif at position -152/-174, a target of proteins of the basic-Helix-Loop-Helix (b-HLH) family including transcription factor USF/MLTF, acts as a downregulator of transcription [Giacca, M. et al. 1992. Virology 186, 133-147] and is constitutively occupied in living cells by in vivo footprinting [Demarchi et al. 1992 J. Virol. 66, 2514-2518]. We have now extended these observations showing that: 1) in transfection studies, mutations of this sequence results in increased transcription efficiency; 2) cotransfection of an expression vector for USF/MLTF results in downregulation of LTR expression; 3) in the murine FR3T3 cell line over expressing USF/MLTF, developed in our laboratory, LTR transcriptional strength is decreased. All these data indicate that the b-HLH box of the LTR is the target of trans-acting factors with repressor activity and that USF/MLTF participates in this function. Strikingly, however, USF/MLTF is a positive regulator in most of the other biological systems. Furthermore, a fusion protein, containing the GAL4 binding domain fused to the USF/MLTF activator domain, behaves as an upregulator from a reporter LTR in which the USF/MLTF site has been mutated to a GAL4 site. Therefore, we are currently pursuing the hypothesis that the downregulator activity of native USF/MLTF could be exerted by the interaction with another factor(s) through the dimerization motif of the protein, which is lost in the GAL4 fusion protein.
Publication Types:
Keywords:
- Base Sequence
- Binding Sites
- DNA-Binding Proteins
- HIV-1
- Helix-Turn-Helix Motifs
- Humans
- Terminal Repeat Sequences
- Transcription Factors
- Transcription, Genetic
- genetics
Other ID:
UI: 102202875
From Meeting Abstracts