Recombinant Saccharomyces cerevisiae Midasin (MDN1), partial

Nuclear chaperone required for maturation and nuclear export of pre-60S ribosome subunits. Functions at successive maturation steps to remove ribosomal factors at critical transition points, first driving the exit of early pre-60S particles from the nucleolus and then driving late pre-60S particles from the nucleus. At an early stage in 60S maturation, mediates the dissociation of the NOP7 complex (YTM1-ERB1-NOP7) from early pre-60S particles, rendering them competent for export from the nucleolus to the nucleoplasm. Subsequently recruited to the nucleoplasmic particles through interaction with the RIX1 complex. This binding is only possible if the 5S RNP at the central protuberance has undergone the rotation to complete its maturation. After remodeling, removes the ribosome biogenesis factor RSA4 in an ATP hydrolysis-driven step from pre-60S ribosomal subunits, rendering them competent for export from the nucleoplasm to the cytoplasm. Activates the GTPase activity of NOG2, which disengages from the pre-60S particle upon GTP hydrolysis, thus freeing its binding site for the nuclear export factor NMD3.