Purification and properties of the NusB protein of Escherichia coli.
Mutations in the nusB gene of Escherichia coli block transcriptional antitermination mediated by the N gene protein of bacteriophage lambda. We describe here two methods of overproducing the NusB protein in E. coli and a method of purifying NusB to apparent homogeneity on a large scale. Purified NusB directly stimulates transcriptional antitermination by the lambda N protein in vitro. It behaves as a monomer (Mr = 15,689) during gel permeation chromatography and gradient sedimentation. The number of NusB molecules in a wild type E. coli K12 cell ranges from about 3,000 to about 6,000 molecules/cell, depending on the growth medium, and is about 50-80% of the number of molecules of the core component of RNA polymerase in the cell. This implies that NusB has a major role in regulating chain elongation during the transcription of E. coli genes. Many E. coli strains with nusB mutations cannot grow at low temperature. However, a sup+ strain with the suppressible amber mutation nusBam115 can grow at 42 degrees C. Since such a strain does not produce NusB protein detectable by immunoprecipitation with anti-NusB, normal amounts of NusB are not essential for the survival of E. coli at 42 degrees C.
Swindle
J
J
Department of Cellular, Viral and Molecular Biology, University of Utah School of Medicine, Salt Lake City 84132.
Zylicz
M
M
Georgopoulos
C
C
Li
J
J
Greenblatt
J
J
D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification*; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005796:Genes; D005798:Genes, Bacterial; D009154:Mutation; D014158:Transcription, Genetic
D001426:Bacterial Proteins