Rna14-Rna15 assembly mediates the RNA-binding capability of Saccharomyces cerevisiae cleavage factor IA

The Rna14–Rna15 complex is a core component of the cleavage factor IA RNA-processing complex from Saccharomyces cerevisiae. To understand the assembly and RNA-binding properties, we have isolated and characterized the Rna14–Rna15 complex using a combination of biochemical and biophysical methods. Analysis of the purified complex, using transmission electron microscopy, reveals that the two proteins assemble into a kinked rod-shaped structure and that these rods are able to further self-associate. Analytical ultracentrifugation reveals that Rna14 mediates this association and facilitates assembly of an A₂B₂ tetramer (M_r 230000), where relatively compact Rna14–Rna15 heterodimers are in rapid equilibrium with tetramers that have a more extended shape. The Rna14–Rna15 complex, unlike the individual components, binds to an RNA oligonucleotide derived from the 3′-untranslated region of the S.cerevisiae GAL7 gene. Based on these structural and thermodynamic data, we propose that CFIA assembly regulates RNA-binding activity.