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J. Virol., Dec 1995, 7559-7569, Vol 69, No. 12
S Baskerville, M Zapp and AD Ellington
Interactions between the Rex protein of HTLV-1 and the genomic Rex- binding
element (XBE) mediate the cytoplasmic transport of viral mRNAs. However, it
is uncertain which RNA sequences and structures contribute to Rex
recognition. A portion of the viral genome that spanned the XBE was
partially randomized, and functional Rex-binding variants were selected.
Alignment of selected Rex-binding sequences revealed positions that were
functionally conserved between different molecules. A model is presented in
which a subset of the selected residues are in direct contact with Rex.
Positions that covaried with one another were also found. These
covariations support a secondary-structural model in which a central paired
stem is symmetrically flanked by two bulge loops. On the basis of this
model, site-directed mutations of the XBE were constructed and each half
molecule was found to bind independently to Rex. The functional residues
and secondary structures in the XBE half molecules bear a remarkable
resemblance to the transactivation response region element of HIV-1. Since
the transactivation response region element is known to interact
specifically with arginine residues in the Tat protein, these results
suggest that the XBE binds to the arginine-rich RNA-binding domain of Rex
in a similar manner. This model is supported by the selection data.
Copyright © 1995, American Society for Microbiology
High-resolution mapping of the human T-cell leukemia virus type 1 Rex- binding element by in vitro selection
Department of Chemistry and Microbiology, Indiana University, Bloomington 47405, USA.
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