Ribosomes, the organelles that catalyze protein synthesis, are composed of a small subunit (40S) and a large subunit (60S) that consist of over 80 distinct ribosomal proteins. Mammalian ribosomal proteins are encoded by multigene families that contain processed pseudogenes and one functional intron-containing gene within their coding regions. Ribosomal Protein L3, also known as RPL3 or TARBP-B, is a 403 amino acid protein that localizes to the cytoplasm and belongs to the L3P family of ribosomal proteins. Expressed as multiple alternatively spliced isoforms, Ribosomal Protein L3 is able to bind to HIV-1 mRNA, possibly activating HIV-1 protein translation. Like most ribosomal proteins, Ribosomal Protein L3 exists as multiple processed pseudogenes that are scattered throughout the genome.