The exozyme model: a continuum of functionally distinct complexes.

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• Exosome complexes, comprising 10-11 subunits, are central to RNA processing and turnover.
• The established model proposes a single, stoichiometric core exosome performs all in vivo RNA metabolic functions.
• Existing data challenge the uniformity of the core exosome model in vivo.

Purpose of the Study:

• To evaluate the current core exosome model against available evidence.
• To propose a novel model that better explains exosome function and regulation.
• To provide a new framework for understanding RNA processing and turnover.

Main Methods:

• Review of genetic, cell biological, proteomic, and transcriptomic data.
• Analysis of predictions derived from the current core exosome model.
• Formulation of the alternative exozyme hypothesis.

Main Results:

• The current core exosome model's predictions are not fully supported by existing evidence.
• Subsets of exosome subunits and cofactors can form distinct complexes (exozymes).
• These exozymes exhibit different RNA specificities, explaining diverse RNA metabolic functions.

Conclusions:

• The exozyme hypothesis offers a more comprehensive explanation for exosome function than the uniform core model.
• Exosome subunits can function both within the core complex and in distinct exozyme assemblies.
• This revised model provides a new framework for studying RNA processing, turnover, and regulation.