Escherichia coli RNase M is a multiply altered form of RNase I

Area of Science:

• Molecular Biology
• Bacteriology

Background:

• RNase M was previously identified as a distinct endoribonuclease in Escherichia coli, thought to be responsible for mRNA degradation.
• Its unique properties suggested it was a separate low molecular mass, broad specificity enzyme from RNase I.

Purpose of the Study:

• To investigate the true identity and relationship of RNase M to other endoribonucleases in E. coli.
• To determine if RNase M represents a novel enzyme or a modified form of an existing one.

Main Methods:

• Sequence analysis of the RNase M gene and protein.
• Southern hybridization to examine gene structure.
• Enzyme activity assays to compare RNase M and RNase I functions.

Main Results:

• Sequence analysis revealed RNase M is a mutated form of RNase I, with three amino acid substitutions.
• The gene encoding RNase M contains a UGA nonsense codon, indicating potential readthrough during translation.
• RNase M exhibits properties conferred by these alterations, distinguishing it functionally from wild-type RNase I.

Conclusions:

• RNase M is not a distinct enzyme but a modified variant of RNase I.
• Several previously identified endoribonuclease activities in E. coli may also be manifestations of RNase I.
• This research clarifies the RNase landscape in E. coli, consolidating multiple activities under RNase I.