Abstract
The effect of structural changes on the functions of the RNA component (M1 RNA) of ribonuclease P (RNase P) of Escherichia coli has been studied using the thermosensitive mutants of the rnpB gene. One of the mutants, ts709, has two G--A substitutions at positions 89 and 365 from the 5' end of M1 RNA. Of these substitutions, the one at position 89 from the 5' end is responsible for the phenotype of this mutant. Although the RNase P activity of ts709 is thermosensitive, the mutant M1 RNA has the same catalytic activity as the wild-type RNA. M1 RNA of another mutant, ts2418, has a G--A substitution at position 329. This mutant RNA has extremely low catalytic activity. The upstream mutational site of ts709 appears to play a role in the association with the protein subunit, whereas the mutational site of ts2418 is related to the catalytic function of M1 RNA.