RBMX is a component of the centromere noncoding RNP complex involved in cohesion regulation

Satellite I RNA, a noncoding (nc)RNA transcribed from repetitive regions in human centromeres, binds to Aurora kinase B and forms a ncRNP complex required for chromosome segregation. To examine its function in this process, we purified satellite I ncRNP complex from nuclear extracts prepared from asynchronized or mitotic (M) phase-arrested HeLa cells and then carried out LC/MS to identify proteins bound to satellite I RNA. RBMX (RNA-binding motif protein, X-linked), which was isolated from M phase-arrested cells, was selected for further characterization. We found that RBMX associates with satellite I RNA only during M phase. Knockdown of RBMX induced premature separation of sister chromatid cohesion and abnormal nuclear division. Likewise, knockdown of satellite I RNA also caused premature separation of sister chromatids during M phase. The amounts of RBMX and Sororin, a cohesion regulator, were reduced in satellite I RNA-depleted cells. These results suggest that satellite I RNA plays a role in stabilizing RBMX and Sororin in the ncRNP complex to maintain proper sister chromatid cohesion.