Mutational analysis of a ribonuclease III processing signal

Area of Science:

• Molecular Biology
• RNA Processing
• Enzymology

Background:

• Ribonuclease III (RNase III) is a crucial enzyme in RNA processing.
• The bacteriophage T7 R1.1 processing signal is a model substrate for studying RNase III activity.
• Understanding the structural requirements for RNase III cleavage is essential for deciphering gene regulation.

Purpose of the Study:

• To identify sequence and structural elements of the T7 R1.1 RNA processing signal critical for RNase III enzymatic cleavage.
• To investigate the role of the internal loop and stem structures in RNase III substrate recognition and cleavage.
• To elucidate how mutations affect RNase III binding affinity and cleavage selectivity.

Main Methods:

• A mutational approach was used to generate variants of the T7 R1.1 RNA processing signal.
• In vitro enzymatic cleavage assays were performed to assess processing reactivity and selectivity.
• Gel electrophoretic mobility shift assays (EMSAs) were employed to study RNase III-RNA complex formation.

Main Results:

• Altering dsRNA stem length did not change cleavage site but decreased reactivity.
• Specific point mutations disrupting stem base-pairing maintained accurate processing.
• A WC base-paired internal loop allowed efficient cleavage at an alternative site and increased RNase III binding affinity.

Conclusions:

• The internal loop of the T7 R1.1 signal is not essential for RNase III processing reactivity.
• Disrupting stem base-pairing enhances RNase III binding but can lead to alternative cleavage events.
• The internal loop's function may be to ensure single, canonical cleavage at the expense of binding affinity.