Component of the ribosome, a large ribonucleoprotein complex responsible for the synthesis of proteins in the cell. The small ribosomal subunit (SSU) binds messenger RNAs (mRNAs) and translates the encoded message by selecting cognate aminoacyl-transfer RNA (tRNA) molecules. The large subunit (LSU) contains the ribosomal catalytic site termed the peptidyl transferase center (PTC), which catalyzes the formation of peptide bonds, thereby polymerizing the amino acids delivered by tRNAs into a polypeptide chain. The nascent polypeptides leave the ribosome through a tunnel in the LSU and interact with protein factors that function in enzymatic processing, targeting, and the membrane insertion of nascent chains at the exit of the ribosomal tunnel. Seems involved in the regulation of cell proliferation (PubMed:19392710). Essential in leaf polarity establishment, probably having a role for translation in leaf dorsoventral patterning to specify leaf adaxial identity (PubMed:18305008, PubMed:18305007). Component of the large ribosomal subunit (LSU). A number of isoforms are produced. According to EST sequences. Expressed in seedlings, roots, stems, leaves, inflorescences and siliques. Detected in the embryo and leaf primordia at earlier developmental stages (PubMed:18305007). In reproductive organs, expressed in the inflorescence meristem, floral primordia and four types of young floral organs (PubMed:18305007). Moderate reduction in cell number (PubMed:19392710). Slightly pointed leaves and prominent marginal serrations (PubMed:18305008). Delayed leaf growth and abnormal leaf patterning, with the abaxial mesophyll features appearing in the adaxial mesophyll domain (PubMed:18305007). More proximal vein branching in the petiole and reduced number of small veins at later leaf developmental stages (PubMed:18305007). Abnormal inflorescences terminating early and producing several secondary inflorescences (PubMed:18305007). Double mutant ae6-1 as2-101 exhibits an increased number of lotus- and needle-like leaves, rough adaxial surface of expanded leaves (PubMed:18305007). Double mutants oli2 oli5 have further reduced cell number but exhibit also excessive postmitotic cell enlargement in leaves (compensation phenotype) (PubMed:19392710). Plant missing both OLI5 and GIF1/AN3 have a strong compensation phenotype (PubMed:19392710). The double mutant as1 pgy3 exhibits narrow and elongated leaves with adaxial ectopic lamina (PubMed:18305008). The double mutant ae6 as1/2 produces severe abaxialized leaves (PubMed:18305007). Belongs to the universal ribosomal protein uL18 family.