Artificial regulation of gene expression in Escherichia coli by RNase P

Plasmids encoding various external guide sequences (EGSs) were constructed and inserted into Escherichia coli. In strains harboring the appropriate plasmids, the expression of fully induced β-galactosidase and alkaline phosphatase activity was reduced by more than 50%, while no reduction in such activity was observed in strains with nonspecific EGSs. The inhibition of gene expression was virtually abolished at restrictive temperatures in strains that were temperature-sensitive for RNase P (EC 3.1.26.5). Northern blot analysis showed that the steady-state copy number of EGS RNAs was several hundred per cell in vivo. A plasmid that contained a gene for M1 RNA covalently linked to a specific EGS reduced the level of expression of a suppressor tRNA that was encoded by a separate plasmid. Similar methods can be used to regulate gene expression in E. coli and to mimic the properties of cold-sensitive mutants.