The (p)ppGpp-binding GTPase Era promotes rRNA processing and cold adaptation in Staphylococcus aureus

Area of Science:

• Molecular Biology
• Bacterial Physiology
• Ribosome Biogenesis

Background:

• Ribosome assembly cofactors, including ribosome-associated GTPases (RA-GTPases), are essential for coordinating ribosome biogenesis across life.
• The RA-GTPase Era in Staphylococcus aureus was previously identified as a target of the stringent response alarmone (p)ppGpp, with binding inhibiting its GTPase activity.
• The precise role of Era in ribosome assembly remains unclear, despite its conservation and essentiality in many bacterial species.

Purpose of the Study:

• To elucidate the function of the RA-GTPase Era in Staphylococcus aureus ribosome assembly.
• To investigate the interactions of Era with other ribosome assembly factors and its regulation by the stringent response.
• To understand the contribution of Era to bacterial growth and adaptation under stress conditions.

Main Methods:

• Protein interaction studies to identify Era's binding partners.
• Assessment of Era's role in 30S ribosomal subunit assembly.
• Analysis of growth phenotypes at suboptimal temperatures and rRNA processing.
• Investigation of interactions between Era, CshA, and RelSau, and their impact on enzymatic activities.

Main Results:

• Era is not essential but important for 30S ribosomal subunit assembly in S. aureus.
• Era interacts with the 16S rRNA endonuclease YbeY and the DEAD-box RNA helicase CshA.
• Both Era and CshA are required for growth at suboptimal temperatures and for proper rRNA processing.
• Era and CshA directly interact with the (p)ppGpp synthetase RelSau; RelSau positively affects Era's GTPase activity but negatively impacts CshA's helicase activity.

Conclusions:

• In its GTP-bound form, Era functions as a hub protein on the ribosome, directing rRNA processing/degradation and subunit assembly enzymes.
• Stringent response components impede Era's function, contributing to the slowed growth phenotype observed during this stress response.
• Era and CshA play critical roles in maintaining ribosome assembly and growth under suboptimal conditions, with their activities modulated by the stringent response.