Purification of the NusB gene product of Escherichia coli K12.

The nucleotide sequence of the entire nusB gene of Escherichia coli has recently been determined and the amino acid sequence of its product deduced (Ishii et al. 1984; Swindle et al. 1984). The NusB protein was purified by chromatography on Sephadex G-100, phosphocellulose and hydroxylapatite. Purification of the protein was monitored using 14C-labelled NusB protein, which was synthesized in a maxicell containing an nusB plasmid as a marker. The final product, which was at least 95% pure as judged by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate, had a molecular weight of about 16,000 and an isoelectric point of about 7.3. Analytical data on the amino acid composition of the purified protein agreed with that deduced from the DNA sequence and indicated that this protein was indeed the product of the nusB gene.