The yeast hnRNP-like proteins Yra1p and Yra2p participate in mRNA export through interaction with Mex67p

Yra1p is an essential nuclear protein which belongs to the evolutionarily c onserved REF (RNA and export factor binding proteins) family of hnRNP-like proteins. Yra1p contributes to mRNA export in vivo and directly interacts w ith RNA and the shuttling mRNP export receptor Mex67p in vitro. Here we des cribe a second nonessential Saccharomyces cerevisiae family member, called Yra2p, which is able to complement a YRA1 deletion when overexpressed. Like other REF proteins, Yra1p and Yra2p consist of two highly conserved N- and C-terminal boxes and a central RNP-like RNA-binding domain (RBD). These co nserved regions are separated by two more variable regions, N-vr and C-vr. Surprisingly, the deletion of a single conserved box or the deletion of the RED in Yra1p does not affect viability. Consistently, neither the conserve d N and C boxes nor the RED is required for Mex67p and RNA binding in vitro . Instead, the N-vr and C-vr regions both interact with Mex67p and RNA. We further show that Yra1 deletion mutants which poorly interact with Mex67p i n vitro affect the association of Mex67p with mRNP complexes in vivo and ar e paralleled by poly(A)(+) RNA export defects. These observations support t he idea that Yra1p promotes mRNA export by facilitating the recruitment of Mex67p to the mRNP.