Mutagens are chemical or physical agents that increase the frequency of mutations. Essentially all mutagens show some specificity for the type of mutations produced. The following table indicates the type of mutations typically produced by some useful mutagens.

Mutagen	Mechanism	Types of mutations produced
Spontaneous	DNA replication and repair errors, spontaneous modification of nucleotides	All types of mutations produced
UV irradiation	Pyrimidine dimers induce error prone repair (SOS)	Mainly G-C to A-T transitions, but all other types of mutations including deletions, frameshifts, and rearrangements at somewhat lower frequency
2-aminopurine (2AP)	Base analog	A-T to G-C and G-C to A-T transitions
Bromouracil	Base analog	G-C to A-T and A-T to G-C transitions
Hydroxylamine (NH2OH)	Alkylating agent, generates N4-hudroxycytosine	G-C to A-T transitions when used in vitro
N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)	Alkylating agent, generates O6-methylguanine	G-C to A-T transitions, multiple, closely spaced mutations common
Ethylmethane sulfonate (EMS) (EMS)	Alkylating agent, generates O6-methylguanine	G-C to A-T transitions
Ethylethane sulfonate (DES)	Alkylating agent, induces SOS response	G-C to T-A transversions, other base substitution mutations
Nitrous acid	Oxidative deamination	G-C to A-T and A-T to G-C transitions, deletions produced at a lower frequency
ICR-191	Intercalating agent, alkylacridine derivative that stabilizes looped out bases by stacking between them	Frameshifts, mainly additions or deletions in runs of G or C

REFERENCES:

• Foster, P. 1991. in vivo mutagenesis. Methods Enzymol. 204: 114-124.
• Friedberg, E., G. Walker, and W. Siede. 1995. DNA repair and mutagenesis. ASM Press, Washington, DC.
• Miller, J. H. 1992. A short course in bacterial genetics. Cold Spring Harbor Laboratory Press, NY.
• Roth, J. R. 1970. Genetic techniques in studies of bacterial metabolism. Methods Enzymol. 17: 1-35.