Transcriptional termination factor rho, the alpha subunit of RNA polymerase (RNA nucleotidyltransferase nucleosidetriphosphate: RNA nucleotidyltransferase, EC 2.7.7.6), and ribosomal protein S6 were resolved from whole-cell extracts of E. coli B/r by a high-resolution, two-dimensional polyacrylamide gel electrophoretic technique, and were identified through coelectrophoresis with the purified proteins. The regulation of rho, alpha, and S6 was studied, in steady-state cultures of E. coli B/r growing at rates ranging from 0.6 to 2.1 generations per hr, through the use of this gel technique and a double radioisotope labeling procedure. The regulatory patterns of rho and alpha are distinct from, but similar to, one another. Neither rho nor alpha shows the sharply increasing levels with increasing growth rate shown by the ribosomal proteins was exemplified by S6. The difference between the levels of rho and alpha, on the one hand, and S6, on the other, is most pronounced during rapid growth. The regulatory pattern of alpha is interesting, given the recent suggestion that the gene coding for alpha is contranscribed with genes coding for ribosomal proteins.
