Identification of a Human T-cell Leukemia Virus Type I Tax Peptide in Contact with DNA

Amy L Kimzey,William S Dynan

doi:10.1074/jbc.274.48.34226

Abstract

The human T-cell leukemia virus Tax protein directs binding of a host factor, cAMP response element binding protein, to an extended recognition sequence in the proviral promoter. Prior cross-linking experiments have revealed that Tax makes restricted contact with this DNA at two symmetric positions, 14 nucleotides apart on opposite strands of the DNA. Tax lacks a conventional DNA binding domain, and the sequences in Tax that are in contact with DNA have not been previously identified. Analysis of cross-linked peptides now shows that the contact occurs between Tax residues 89 and 110, corresponding to a protease-sensitive linker joining two protein structural domains. The linker assumes a protease-resistant conformation in the cross-linked complex. Point mutations within the linker prevent cross-linking and interfere with Tax function. These data suggest that entry of Tax into the ternary complex may be coupled to folding of an unstructured protein domain, which then makes base-specific contacts with DNA.

Highlights

Viruses are intracellular parasites that depend on the host cell biosynthetic apparatus to survive
Biochemical studies suggest that Tax activates proviral transcription, in large part, through an interaction with the host cAMP response element binding protein (CREB)
When Tax enters into a ternary complex with CREB and DNA, this loop becomes inaccessible to proteases, and we suggest that it folds into a defined conformation in order to make base-specific contacts within the 5Ј and 3Ј regions of the extended recognition site

Summary

Introduction

Viruses are intracellular parasites that depend on the host cell biosynthetic apparatus to survive. The HTLV-I encoded Tax protein recruits host cell transcription factors to the proviral promoter, leading to high levels of viral RNA synthesis [3,4,5,6,7,8,9,10,11,12,13]. Biochemical studies suggest that Tax activates proviral transcription, in large part, through an interaction with the host cAMP response element binding protein (CREB). Cross-linking studies show that Tax itself makes two extremely restricted DNA contacts within the complex [23] These contacts are arranged symmetrically, 14 nucleotides apart, on opposite strands of the DNA. The formation of a Tax-CREB-DNA ternary complex at the proviral site is made even more significant because of an accompanying change in the interaction of CREB with the transcriptional coactivator, CBP. The interaction of Tax with the TxRE DNA is a key event in the viral life cycle

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