Regulation of ribonucleic acid synthesis in Escherichia coli B-r: an analysis of a shift-up. 1. Ribosomal RNA chain growth rates

The chain growth rate for ribosomal RNA was determined for Escherichia coli$\text{B}\text{r}$ growing in succinate (μ = 0.69 doublings/h), glucose (μ = 1.36) and glucose/ amino acids (μ = 2.10) medium. With increasing bacterial growth rate the chain growth rate increases from 4400 to 6300 nucleotides/min. These values are almost twofold higher than the chain growth rate reported for messenger RNA; this implies that, following a nutritional shift-up, the transfer of a relatively small number of RNA polymerase molecules from unstable to stable RNA genes along with the increase in the stable RNA chain growth rate is sufficient to account for the abrupt increase in the net rate of RNA synthesis. Furthermore, our calculations indicate that the linear density of polymerase molecules on the ribosomal DNA template increases with the bacterial growth rate, such that in rapidly growing bacteria all ribosomal RNA genes (48 copies at μ = 3) are nearly saturated with RNA polymerase.