Sirtuin 7 promotes 45S pre-rRNA cleavage at site 2 and determines the processing pathway

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Ribosome biogenesis is essential for cell growth and occurs in the nucleolus.
• Two alternative pre-rRNA processing pathways exist in humans.
• The role of nucleolar sirtuin 7 in ribosome synthesis was previously unclear.

Purpose of the Study:

• To investigate the function of sirtuin 7 in pre-rRNA processing and ribosome biogenesis.
• To determine how sirtuin 7 activity affects the two alternative processing pathways.
• To elucidate the molecular interactions of sirtuin 7 during ribosome synthesis.

Main Methods:

• Inhibition of sirtuin 7 activity using sirtinol.
• Depletion of sirtuin 7 protein via genetic methods.
• Analysis of pre-rRNA processing intermediates.
• Co-immunoprecipitation to study protein interactions.

Main Results:

• Sirtuin 7 activity regulates the processing of 45S, 32S, and 30S pre-rRNAs.
• Sirtuin 7 is essential for 45S pre-rRNA cleavage at site 2, a key step in processing pathway 2.
• Sirtuin 7 interacts with Nop56 and fibrillarin, potentially interfering with fibrillarin-dependent cleavage.
• Sirtuin 7 depletion leads to accumulation of extended 32S pre-rRNA and altered fibrillarin localization.

Conclusions:

• Sirtuin 7 is a critical regulator of pre-rRNA processing and ribosome biogenesis.
• Sirtuin 7's interaction with fibrillarin suggests a role in determining the pre-rRNA processing pathway.
• These findings establish a link between sirtuin 7, fibrillarin, and the choice of ribosome biogenesis pathway.