Primary structure of Escherichia coli ribosomal protein L31

Protein L31 from the 50S ribosomal subunit of Escherichia coli was manually sequenced by the dansyl-Edman method. Owing to the availability of only small quantities of purified L31, sequencing methods were scaled down such that the entire primary structure could be determined with 700 microgram of protein. The techniques employed are described in detail. The protein consists of a single chain of 62 amino acids, with a calculated molecular weight of 6967. Four half-cystine residues were identified at positions 16, 18, 37, and 40. Evidence is presented that suggests that these residues form two disulfide bridges in the protein, as isolated.