A gene affecting accumulation of the RNA moiety of the processing enzyme RNase P

The level of 10Sb (M1) RNA, the RNA of RNase P, is very low in growing cultures of rnpB mutants. Northern transfer experiments suggested that these strains accumulate no more than 10% of the wild-type level of 10Sb RNA. However, there is no indication that there is a limiting amount of RNase P activity in these mutants in vivo. A plasmid that directs the synthesis of 10Sb RNA does not complement the rnpB mutants, even though there is only a single gene for 10Sb RNA in the Escherichia coli genome. The 10Sb RNA synthesized from this plasmid is equivalent to wild-type 10Sb RNA since it can replace it in the reconstitution of RNase P. The 10Sb RNA, which is a rather stable molecule, is unstable in the presence of the rnpB mutation. This could explain why rnpB mutants do not accumulate 10Sb RNA. An F' plasmid that contains DNA from the rnpB region of the chromosome complements an rnpB mutant in vivo and in vitro, and it also contains the 10Sb RNA gene. A number of possible explanations for these phenomena are discussed.