Some ribosomal proteins may be nonessential and evolve later in the biogenesis of ribosome

Our current understanding of ribosome posits that almost all ribosomal proteins are essential in structure and function to the modern ribosome. However, analysis of the complement of ribosomal proteins in the large and small ribosome subunits of different bacterial, archaeal, and eukaryotic species revealed that many ribosomal proteins do not uniformly exist in all profiled species. This suggests that these ribosomal proteins may be nonessential to the structure and function of the ancestral ribosome, and evolved later in the biogenesis of the modern ribosome. These nonessential ribosomal proteins are ribosomal protein L7Ae, L8, L9, L10, L13, L16, L17, L18, L20, L23, L25, L26, L27, L28, L30, L32, L33, L34, L35, L36, S8, S9, S10, S12, S13, S14, S15, S16, S18, S20, and S21. Overall, revelations made in this work have important implications to our understanding of ribosomal protein evolution, and offer us a glimpse into the possible structure and function of the ancestral ribosome. The work also highlights that the small and large subunit of the ancestral ribosome likely differ in structure and function to the modern ribosome, and implies that ribosomal complexity evolve with changing environmental conditions in the biosphere.