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 introncontaining gene within their coding regions. Ribosomal Protein L39 (RPL39), also known as 60S Ribosomal Protein L39, consists of 51 amino acids and is the smallest protein found in liver ribosomes. Ribosomal Protein L39 localizes to cytoplasm and is a member of the S39E family of ribosomal proteins. The gene encoding Ribosomal Protein L39 maps to human chromosome Xq24, and shares 92 percent homology with Ribosomal Protein L39L (Ribosomal Protein L39-like), which is also known as RPL39L, L39-2 or RPL39L1. Ribosomal Protein L39L is associated with the 60S ribosomal subunit and is expressed in testis with localization in nucleolus.