Quantitation of RNA polymerase subunits in Escherichia coli during exponential growth and after bacteriophage T4 infection

Summary A method was developed to measure the amounts of RNA polymerase subunits, , , and in crude extracts of Escherichia coli. The proteins were labelled by growing the cells in ³⁵S-sulphate containing media. For measuring and , the cell lysate was electrophoresed on 6% polyacrylamide gels containing SDS and the and bands cut out and counted. For measuring and , the cell lysate was co-electrophoresed with dansylated RNA polymerase on 8% polyacrylamide gels containing SDS. The fluorescent bands were cut out, the proteins eluted, and the and subunits further purified on polyacrylamide gels containing 8 molar urea.The results are: (1) is the subunit of the core RNA polymerase which is present in limiting amount. (2) The core enzyme, as measured by , constitutes a constant fraction of total cellular protein (0.9%), independent of the bacterial growth rate. (3) The subunit is made in excess and is probably regulated independently. (4) The subunit is present in 0.3–0.4 times the amount of the core enzyme. (5) All four subunits are fully conserved after bacteriophage T4 infection.