Abstract
Ribosomes are essential for protein synthesis in all organisms and their biogenesis and number are tightly controlled to maintain homeostasis in changing environmental conditions. While ribosome assembly and quality control mechanisms have been extensively studied, our understanding of ribosome degradation is limited. In yeast or animal cells, ribosomes are degraded after transfer into the vacuole or lysosome by ribophagy or nonselective autophagy, and ribosomal RNA can also be transferred directly across the lysosomal membrane by RNautophagy. In plants, ribosomal RNA is degraded by the vacuolar T2 ribonuclease RNS2 after transport by autophagy-related mechanisms, although it is unknown if a selective ribophagy pathway exists in plants. In this review, we describe mechanisms of turnover of ribosomal components in animals and yeast, and, then, discuss potential pathways for degradation of ribosomal RNA and protein within the vacuole in plants.
Highlights
The ribosome is a complex macromolecular machine that is comprised of proteins and RNA.In yeast, it is estimated that ribosomes contain almost 80% of the total cellular RNA and they occupy about 40% of the cytoplasmic volume [1], placing them among the most abundant cellular components
We have a limited understanding of the ribosome turnover process, which involves a tight cooperation between protein degradation and RNA decay and uses mechanisms that span from the cytoplasm to the vacuole or lysosome, and many seemingly contradictory findings need to be reconciled
Further analyses confirmed that NUFIP1, which was previously known as a nucleocytoplasmic shuttling protein regulating the assembly of ribonucleoproteins (RNPs) [24,25,26], redistributes from the nucleus to lysosomes upon mTORC1 inhibition or nutrient deprivation in an autophagosome-dependent manner [18]
Summary
The ribosome is a complex macromolecular machine that is comprised of proteins and RNA. It is estimated that ribosomes contain almost 80% of the total cellular RNA and they occupy about 40% of the cytoplasmic volume [1], placing them among the most abundant cellular components. A large body of work has focused on the ribosome assembly and surveillance and quality control mechanisms for both the protein and RNA components that ensure production of functional ribosomes [2]. We have a limited understanding of the ribosome turnover process, which involves a tight cooperation between protein degradation and RNA decay and uses mechanisms that span from the cytoplasm to the vacuole or lysosome, and many seemingly contradictory findings need to be reconciled. First, we discuss the turnover of ribosomal components in animals and yeast, and, we examine evidence for degradation of ribosomal RNA and protein within the vacuole in plants
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