Mitochondrial ribosome assembly in Neurospora crassa. Purification of the mitochondrially synthesized ribosomal protein, S-5.

In Neurospora, one mitochondrial ribosomal protein (S-5, Mr = 52,000) is synthesized intramitochondrially and is presumably encoded by mitochondrial DNA. We have developed a rapid method for the purification of S-5 which takes advantage of its high affinity for carboxymethyl-Sepharose in the presence of 6 M urea. Using this method, S-5, at purity greater than 95%, can be prepared by column chromatography in a single batch elution step. The amino acid composition of S-5 was determined. Judged by the contents of hydrophilic and basic amino acids, S-5 is more similar to Escherichia coli and yeast ribosomal proteins than to other mitochondrial translation products which are hydrophobic membrane proteins.