Components of an interdependent unit within the SSU processome regulate and mediate its activity.

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• The Small SubUnit (SSU) processome is essential for synthesizing the 18S ribosomal RNA, a key component of the small ribosomal subunit.
• The U3 small nucleolar RNA (snoRNA) within the SSU processome is critical for forming the central pseudoknot and processing pre-ribosomal RNA (pre-rRNA), both necessary for 18S rRNA maturation.

Purpose of the Study:

• To investigate the regulatory and mechanistic functions of U3-specific proteins Imp3p, Imp4p, and Mpp10p in the SSU processome.
• To elucidate the interdependence of these proteins and their roles in U3 snoRNA-pre-rRNA interactions.

Main Methods:

• Analysis of protein stability and association with U3 snoRNA.
• Investigating the effects of mutations in U3 snoRNA and carboxy-terminal truncations of Mpp10p on pre-rRNA processing and cell growth.
• Utilizing heterologous complementation experiments to assess functional domains of Mpp10p.

Main Results:

• Imp3p, Imp4p, and Mpp10p exhibit interdependence in stability and binding to U3 snoRNA.
• Mutations affecting U3 snoRNA-pre-rRNA processing and Mpp10p truncations lead to similar growth and processing defects.
• Mpp10p appears to be involved in maintaining U3 snoRNA-pre-rRNA base pairing and an additional mechanistic step at cleavage site A(2).
• The C-terminal 95 amino acids of yeast Mpp10p are specifically required for growth and pre-rRNA processing at low temperatures.

Conclusions:

• The U3-specific proteins Imp3p, Imp4p, and Mpp10p are crucial for SSU processome function, exhibiting interdependent stability and snoRNA association.
• Mpp10p plays a multifaceted role in pre-rRNA processing, including facilitating U3 snoRNA-pre-rRNA base pairing and participating in cleavage events.
• Specific domains of Mpp10p are essential for its function, particularly under suboptimal growth conditions.