Pre60S

Pre60S refers to a class of ribosomal large-subunit maturation intermediates in eukaryotes. These particles form during ribosome biogenesis in the nucleolus and nucleoplasm as they process and assemble the components needed for the 60S subunit. A pre60S particle contains the major ribosomal RNAs of the large subunit (including 5S, 5.8S, and 25/28S) along with a subset of ribosomal proteins and a revolving set of assembly factors that guide folding, processing, and maturation of the ribosomal RNA. The composition of pre60S particles changes as maturation proceeds, with early particles bearing factors that promote proper folding and processing and later particles recruiting export factors and becoming competent for nuclear export.

Export to the cytoplasm is mediated by the nuclear pore complex in a Crm1- and RanGTP-dependent manner. In the cytoplasm, additional maturation steps remove assembly factors and finalize rRNA processing. Energy-dependent remodeling by factors such as the AAA-ATPase Rea1 (MDN1) and the GTPase Efl1 (often with Sdo1) promotes structural rearrangements and factor release. The final maturation includes the release of eIF6 and Nmd3, enabling the mature 60S subunit to participate in translation by joining with a 40S subunit to form the functional 80S ribosome.

Research on pre60S has benefited from studies in model organisms, particularly yeast, which have helped delineate the sequence of assembly stages and quality-control checkpoints. Defects in 60S maturation can disrupt ribosome biogenesis and are linked to ribosomopathies in humans, including conditions such as Shwachman-Diamond syndrome. See also ribosome biogenesis and 60S subunit.