Expansion Segment ES30L enriched in birds and mammals can potentially regulate protein synthesis

Ribosomes, the molecular machines that are central to protein synthesis, have gradually been gaining prominence for their regulatory role in translation. Eukaryotic cytosolic ribosomes are typically larger than bacterial ones, partly due to multi-nucleotide insertions at specific conserved positions in the ribosomal RNAs (rRNAs). Such insertions called expansion segments (ESs) are present primarily on the ribosomal surface, with their role in translation and its regulation remaining under-explored. One such ES in the ribosomal large subunit (LSU) is ES30L, which is present only in mammals and birds among eukaryotes. In this study, we show that ES30L possesses complementarity to many protein-coding transcripts in humans and that the complementarity is enriched around the start codon, hinting at a possible role in translation regulation. Further, our in silico analysis analyses and pull-down assays indicate that ES30L may bind to secondary structures in the 5 UTR of several transcripts and RNA binding proteins (RBPs) that are essential for translation. Thus, we have identified a potential regulatory role for ES30L in translation.