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SOS-inducing ability of native and mutant microbial ribonucleases
O N Ilinskaya1, N S Karamova, O B Ivanchenko
1GENTOX Laboratory, Microbiology Department, Kazan State University, Tatarstan, Russia. olganil@open.ksu.ras.ru
Mutation Research
|July 22, 1996
Summary
High-activity microbial ribonucleases from Bacillus species show genotoxicity, likely via RNA cleavage. Reduced activity or inhibited enzymes lacked this SOS-inducing potency in genotoxicity tests.
Area of Science:
- Microbiology
- Molecular Biology
- Genotoxicology
Background:
- Bacillus species produce microbial ribonucleases (RNases) with varying catalytic activities.
- Site-directed mutagenesis and natural inhibitors can alter RNase function.
- Genotoxicity testing assesses the potential of substances to damage genetic material.
Purpose of the Study:
- To evaluate the genotoxicity of Bacillus-derived RNases with differing catalytic activities.
- To investigate the relationship between RNase catalytic activity and SOS-inducing potential.
- To determine if RNA cleavage is the mechanism underlying RNase genotoxicity.
Main Methods:
- Genotoxicity testing using the SOS chromotest.
- Site-directed mutagenesis to create RNase variants with altered catalytic activity.
- Assessing RNase activity using wild-type, mutant, and inhibitor-inactivated enzymes.
Main Results:
- Wild-type and high-activity mutant RNases (e.g., Arg58Lys binase) showed significant SOS induction (induction factor 1.8-2.8).
- Mutant RNases with reduced catalytic activity (Lys26Ala, Arg61Gln, His101Glu) did not exhibit SOS-inducing potency.
- Inactivated wild-type RNase by barstar also showed no SOS-inducing effects.
Conclusions:
- High catalytic activity of Bacillus RNases correlates with genotoxicity.
- Genotoxicity appears to be mediated by the enzyme's ability to cleave cellular RNA.
- Enzymes with diminished catalytic function or inhibited activity are not genotoxic via this mechanism.