A pre-ribosome with a tadpole-like structure functions in ATP-dependent maturation of 60S subunits.

Analyses of isolated pre-ribosomes yielded biochemical "snapshots" of the dynamic, nascent 60S and 40S subunits during their path from the nucleolus to the cytoplasm. Here, we present the structure of a pre-60S ribosomal intermediate located in the nucleoplasm. A huge dynein-related AAA-type ATPase (Rea1) and the Rix1 complex (Rix1-Ipi1-Ipi3) are components of an extended (approximately 45 nm long) pre-60S particle. Antibody crosslinking in combination with electron microscopy revealed that the Rea1 localizes to the "tail" region and ribosomal proteins to the "head" region of the elongated "tadpole-like" structure. Furthermore, in vitro treatment with ATP induces dissociation of Rea1 from the pre-60S subunits. Rea1 and the Rix1 complex could mediate ATP-dependent remodeling of 60S subunits and subsequent export from the nucleoplasm to the cytoplasm.