T cell intracellular antigen-1 (
TIA-1), an
apoptosis promoting factor, functions as a splicing regulator for the Fas pre-mRNA.
TIA-1 possesses three
RNA recognition motifs (RRMs) and a glutamine-rich domain. The second RRM (RRM2) is necessary and sufficient for tight, sequence-specific binding to the uridine-rich sequences buried around the
5' splice sites. In the present study, we solved the
solution structure of the murine
TIA-1 RRM2 by heteronuclear-nuclear
magnetic resonance spectroscopy. The
TIA-1 RRM2 adopts the RRM fold (betaalphabetabetaalphabeta) and possesses an extra beta-strand between beta2 and beta3, which forms an additional
beta-sheet with the
C-terminal part of beta2. We refer to this structure as the beta2-beta2' beta-loop. Interestingly, this characteristic beta-loop structure is conserved among a number of RRMs, including the U2AF65 RRM2 and the Sex-lethal
RRM1 and RRM2, which also bind to uridine-rich
RNAs. Furthermore, we identified a new
sequence motif in the beta2-beta2' beta-loop, the DxxT motif.
Chemical shift perturbation analyses of both the main and side chains upon binding to the
uridine pentamer RNA revealed that most of the
beta-sheet surface, including the beta2-beta2' beta-loop, is involved in the
RNA binding. An investigation of the
chemical shift perturbation revealed similarity in the
RNA recognition modes between the
TIA-1 and U2AF65 RRMs.
