Conformation of Tax-response elements in the human T-cell leukemia virus type I promoter.
BACKGROUND
HTLV-I Tax is believed to activate viral gene expression by binding bZIP proteins (such as CREB) and increasing their affinities for proviral TRE target sites. Each 21 bp TRE target site contains an imperfect copy of the intrinsically bent CRE target site (the TRE core) surrounded by highly conserved flanking sequences. These flanking sequences are essential for maximal increases in DNA affinity and transactivation, but they are not, apparently, contacted by protein. Here we employ non-denaturing gel electrophoresis to evaluate TRE conformation in the presence and absence of bZIP proteins, and to explore the role of DNA conformation in viral transactivation.


RESULTS
Our results show that the TRE-1 flanking sequences modulate the structure and modestly increase the affinity of a CREB bZIP peptide for the TRE-1 core recognition sequence. These flanking sequences are also essential for a maximal increase in stability of the CREB-DNA complex in the presence of Tax.


CONCLUSIONS
The CRE-like TRE core and the TRE flanking sequences are both essential for formation of stable CREB-TRE-1 and Tax-CREB-TRE-1 complexes. These two DNA segments may have co-evolved into a unique structure capable of recognizing Tax and a bZIP protein.
Cox
J M
JM
Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA.
Sloan
L S
LS
Schepartz
A
A
D051697:Activating Transcription Factor 1; D001345:Autoradiography; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D017977:Deltaretrovirus / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D051790:G-Box Binding Factors; D016356:Gene Products, tax / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
D051697:Activating Transcription Factor 1; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051790:G-Box Binding Factors; D016356:Gene Products, tax; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D004247:DNA