Ethyl methanesulfonate

Ethyl methanesulfonate (EMS) is an organosulfur compound with the formula . It is the ethyl ester of methanesulfonic acid. A colorless liquid, it is classified as an alkylating agent. EMS is the most commonly used chemical mutagen in experimental genetics. Mutations induced by EMS exposure can then be studied in genetic screens or other assays.

Use in biological research

EMS produces random mutations in genetic material by nucleotide substitution; particularly through G:C to A:T transitions induced by guanine alkylation. EMS typically produces only point mutations. Due to its potency and well understood mutational spectrum, EMS can induce mutations at a rate of 5 × 10⁻⁴ to 5 × 10⁻² per gene without substantial killing. A 5 × 10⁻⁴ per gene mutation rate observed in a typical EMS mutagenesis experiment of the model organism C. elegans, corresponds to a raw mutation rate of ~7 × 10⁻⁶ mutations per G/C base pair, or about 250 mutations within an originally mutagenized gamete (containing a ~100 Mbp, 36% GC haploid genome). Such a mutagenized gamete would have about 9 different loss-of-function mutations in genes, with 1 to 2 of these mutations being within essential genes and therefore lethal. However, since it is unlikely the same essential gene is mutated in independent gametes, and if loss of the essential gene did not kill the gamete itself, downstream gamete fusion often allows for survival of the resulting zygote and organism, as the now heterozygous non-functional mutated allele may be rescued by the still wildtype allele provided by the other gamete.

Repair of mutagenic lesion

O⁶-ethylguanine can be repaired in vivo in a stoichiometric fashion by reacting with the active site cysteine of the O-6-methylguanine-DNA methyltransferase repair protein. The in vivo half-life of O⁶-ethylguanine was reported to be about 9 days in mouse brain, while it was about 1 day in mouse liver.

Induction of recombination

EMS induces mitotic recombination in Saccharomyces cerevisiae. It was suggested that EMS damage to DNA may result in a repair process leading to genetic exchange. This finding suggests that a recombination process catalyzed by the proteins specified by these six genes is employed in repairing EMS lethal lesions in DNA. Therefore, EMS must be specifically degraded before disposal. Protocols call for degradation of EMS in an equal volume of a 0.1M NaOH and 20% w/v sodium thiosulfate "inactivating solution", for at least six half-lives (>24 hours).

See also

• Mutagenesis (molecular biology technique)
• MMS
• DMS
• ENU

References