Modification of a Specific Ribosomal Protein Catalyzed by Leucyl, Phenylalanyl-tRNA:Protein Transferase^*

Abstract

Escherichia coli ribosomes washed with 1 M NH₄Cl were found to function as acceptor for leucine and phenylalanine in the reaction catalyzed by leucyl, phenylalanyl-tRNA:protein transferase. When isolated subunits were acylated with [¹⁴C]phenylalanine and reisolated by gradient centrifugation, the recovered 30S particles had a specific radioactivity nearly 30 times that of similarly treated 50S particles. Autoradiography of gels, which contained protein from acylated 30S particles, that had been subjected to electrophoresis in 8 M urea and in sodium dodecyl sulfate, suggested that acceptor activity was largely due to a single protein with a molecular weight of about 12,000. Leucine and phenylalanine residues that had been transferred to ribosomal protein were reactive with fluorodinitrobenzene and were released as leucyl- or phenylalanylarginine after treatment with trypsin.

The results indicate that leucyl, phenylalanyl-tRNA: protein transferase catalyzes the addition of these amino acids to an NH₂-terminal arginine residue of a specific ribosomal protein on the 30S subunit.

• subunits
• gel electrophoresis
• gradient centrifugation
• E. coli