Nucleolin functions in the first step of ribosomal RNA processing

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Ribosome biogenesis is a fundamental cellular process.
• Precursor ribosomal RNA (pre-rRNA) undergoes complex processing, including cleavage in the 5' external transcribed spacer.
• This initial cleavage is conserved across species and involves specific small nucleolar RNAs (snoRNAs).

Purpose of the Study:

• To investigate the role of nucleolin, a major nucleolar RNA-binding protein, in the early processing of pre-rRNA.
• To determine if nucleolin's interaction with pre-rRNA is necessary for processing.
• To explore nucleolin's interaction with U3 snoRNP and its effect on pre-rRNA processing.

Main Methods:

• In vitro processing assays to assess pre-rRNA cleavage.
• RNA-binding experiments to confirm nucleolin-pre-rRNA and nucleolin-U3 snoRNP interactions.
• Analysis of S100 cell extracts with varying nucleolin levels and U3 snoRNA presence.

Main Results:

• Nucleolin directly interacts with the pre-rRNA substrate.
• This interaction is crucial for the in vitro processing of pre-rRNA.
• Nucleolin also interacts with the U3 snoRNP.
• Elevated nucleolin levels, with U3 snoRNA, enhance pre-rRNA processing activity in cell extracts.
• Nucleolin-pre-rRNA interaction appears to be a rate-limiting step in primary processing.

Conclusions:

• Nucleolin is the first identified metazoan protein to directly bind rRNA and be required for its processing.
• Nucleolin plays a critical role in the early cleavage of pre-rRNA.
• The findings suggest a significant role for nucleolin in ribosome biogenesis.