Identification of an amino acid-regulated mRNA from rat liver as the mammalian equivalent of bacterial ribosomal protein L22.

Amino acid deprivation of rat hepatoma cells induced the levels of a 612-base pair mRNA termed ASI (Shay, N. F., Nick, H. S., and Kilberg, M. S. (1990) J. Biol. Chem. 265, 17844-17848). The ASI mRNA was present at levels equal to or greater than actin in every rat tissue tested. The corresponding full-length cDNA was cloned, and the present report demonstrates that the deduced 184-residue amino acid sequence shares greater than 30% identity to a number of bacterial and chloroplast L22 ribosomal proteins, including those from Escherichia coli and Halobacterium halobium. A monospecific anti-peptide antibody was produced that upon immunochemical analysis of subcellular fractions of rat liver recognized a band in the microsomal fraction and, more specifically, reacted with a single polypeptide in the ribosomal large subunit fraction. The antibody did not react with any proteins of the mitochondrial large subunit, but did recognize a protein in human liver homogenate at the same relative mobility (23 kDa) as that observed for rat liver.