The Regulation of TIA‐1 Binding to RNA by pH Conditions

Abstract

TIA-1 is an RNA-binding protein responsible for pre-mRNA splicing and mRNA translation1. TIA-1 is constitued by three RNA recognition motifs (RRMs) and a prion-related domain. The protein binds to single stranded RNAs through its C-terminal RRM domains, the so-called RRM2 and RRM3. RRM2 is primarily responsible for the interaction with RNA, but the RNA sequences recognized by RRM3 are still unknown. We combine NMR, SPR and pull-down assays to elucidate the sequence specificity of RRM3 towards cytosine-enriched oligonucleotides2. We also report that the RNA binding of RRM3 is modulated by protonation of its three histidines, with physiological pKa values3. Although the pKa value of the unique RRM2-histidine is significantly acidic, it becomes biologically relevant upon complexing to RNA4. Our findings reveal the role of RRM3 in regulating TIA-1 binding to C-rich stretches, which are abundant at the 5´Terminal Oligopyrimidine Tracts of translationally-repressed mRNAs5. Moreover, the pKa differences between free RRMs and their complexes with RNA explain the functionality of TIA-1 between the nucleus and the cytoplasm.