Cms1 coordinates stepwise local 90S pre-ribosome assembly with timely snR83 release

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Ribosome synthesis is a complex process initiated in the nucleolus with the formation of the 90S pre-ribosome.
• The precise guidance of small nucleolar RNAs (snoRNAs) to target sites on pre-ribosomal RNA (pre-rRNA) during 90S assembly remains poorly understood.
• Key factors like Rrp12-Enp1 are crucial for 90S pre-ribosome maturation.

Purpose of the Study:

• To investigate the role of Cms1 protein in the timely recruitment of snoRNAs during early ribosome biogenesis.
• To elucidate the mechanism by which Cms1 influences the binding of factors like Rrp12-Enp1 to the 90S pre-ribosome.
• To understand how Cms1 facilitates the modification of pre-rRNA by snoRNAs.

Main Methods:

• Genetic screening to identify suppressors of mutations affecting ribosome synthesis (nop14 mutant).
• Co-immunoprecipitation assays to identify protein interactions within the 90S pre-ribosome.
• Localization studies to determine the association of Cms1 with specific rRNA domains and assembly intermediates.

Main Results:

• Cms1 was identified as a suppressor of a nop14 mutant, indicating a role in 90S assembly.
• Cms1 was detected on the 18S rRNA 3' major domain of early 90S particles containing the H/ACA snoR83.
• Cms1 co-precipitated with multiple 90S factors, and its presence correlated with decreased Rrp12-Enp1 binding in mature 90S particles.

Conclusions:

• Cms1 plays a critical role in regulating the assembly of the 90S pre-ribosome.
• Cms1 likely restricts premature Rrp12-Enp1 binding to the 3' major domain during early 90S biogenesis.
• Cms1 facilitates the timely modification of pre-rRNA by snoR83 before its release and subsequent 90S assembly steps.