ethyl methanesulfonate

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,{{cn|date=January 2025}} EMS can induce mutations at a rate of 5x10⁻⁴ to 5x10⁻² per gene without substantial killing. A 5x10⁻⁴ per gene mutation rate observed in a typical EMS mutagenesis experiment of the model organism C. elegans, corresponds to a raw mutation rate of ~7x10⁻⁶ mutations per G/C base pair, or about 250 mutations within an originally mutagenized gamete (containing a ~100 Mbp, 36% GC haploid genome).{{Cite book |last=Anderson |first=Philip |title=Caenorhabditis elegans: Modern Biological Analysis of an Organism |publisher=Elsevier |year=1995 |isbn=978-0-12-564149-4 |series=Methods in Cell Biology |volume=48 |pages=31–58 |chapter=Chapter 2 Mutagenesis |doi=10.1016/s0091-679x(08)61382-5 |issn=0091-679X}} 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.

The ethyl group of EMS reacts with guanine in DNA, forming the abnormal base O⁶-ethylguanine. During DNA replication, DNA polymerases that catalyze the process frequently place thymine, instead of cytosine, opposite O⁶-ethylguanine. Following subsequent rounds of replication, the original G:C base pair can become an A:T pair (a transition mutation). This changes the genetic information, is often harmful to cells, and can result in disease. RNA polymerase can also place uridine (RNA analog of thymine) opposite an O⁶-ethylguanine lesion.{{Cite journal |last=Gerchman |first=Lois L. |last2=Ludlum |first2=David B. |year=1973 |title=The properties of in templates for RNA polymerase |journal=Biochimica et Biophysica Acta (BBA) - Nucleic Acids and Protein Synthesis |publisher=Elsevier BV |volume=308 |issue=2 |pages=310–316 |doi=10.1016/0005-2787(73)90160-3 |issn=0005-2787 |pmid=4706005}}

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.{{Cite journal |last=Pegg |first=Anthony E |year=2000 |title=Repair of O6-alkylguanine by alkyltransferases |journal=Mutation Research/Reviews in Mutation Research |publisher=Elsevier BV |volume=462 |issue=2–3 |pages=83–100 |doi=10.1016/s1383-5742(00)00017-x |issn=1383-5742 |pmid=10767620}} 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.{{Cite journal |last=Goth |first=R. |last2=Rajewsky |first2=M. F. |date=1974-03-01 |title=Persistence of O6-Ethylguanine in Rat-Brain DNA: Correlation with Nervous System-Specific Carcinogenesis by Ethylnitrosourea |journal=Proceedings of the National Academy of Sciences |volume=71 |issue=3 |pages=639–643 |bibcode=1974PNAS...71..639G |doi=10.1073/pnas.71.3.639 |issn=0027-8424 |pmc=388067 |pmid=4522778 |doi-access=free}}

EMS induces mitotic recombination in Saccharomyces cerevisiae.{{Cite journal |last=Yost Jr |first=H. T. |last2=Chaleff |first2=R. S. |last3=Finerty |first3=J. P. |date=1967 |title=Induction of mitotic recombination in Saccharomyces cerevisiae by ethyl methane sulphonate |journal=Nature |volume=215 |issue=5101 |pages=660–661 |bibcode=1967Natur.215..660Y |doi=10.1038/215660a0 |pmid=6050236 |s2cid=1982778}} It was suggested that EMS damage to DNA may result in a repair process leading to genetic exchange.

Bacteriophage T4 mutants defective in any one of six genes known to be required for genetic recombination were found to be more sensitive to inactivation by EMS than wild type bacteriophage.{{Cite journal |last=Johns |first=V. |last2=Bernstein |first2=C. |last3=Bernstein |first3=H. |date=1978 |title=Recombinational repair of alkylation lesions in phage T4. II. Ethyl methanesulfonate |journal=Molecular & General Genetics |volume=167 |issue=2 |pages=197–207 |doi=10.1007/BF00266913 |pmid=215891 |s2cid=30597383}} 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.

Generally speaking EMS is unstable in water. It hydrolyzes to ethanol and methanesulfonic acid. At neutral to acidic pH at room temperature, it has a fairly long half-life of over 1 day.{{Cite journal |last=FROESE-GERTZEN |first=EDITH E. |last2=KONZAK |first2=C. F. |last3=FOSTER |first3=R. |last4=NILAN |first4=R. A. |year=1963 |title=Correlation between Some Chemical and Biological Reactions of Ethyl Methanesulphonate |journal=Nature |publisher=Springer Science and Business Media LLC |volume=198 |issue=4879 |pages=447–448 |bibcode=1963Natur.198..447F |doi=10.1038/198447a0 |issn=0028-0836 |s2cid=12359460}}{{Cite book |last=Kodym |first=Andrea |title=Plant functional genomics |last2=Afza |first2=Rownak |publisher=Humana Press |year=2003 |isbn=978-1-58829-145-5 |publication-place=Totowa, N.J |pages=189–203 |chapter=Chapter 12 Physical and Chemical Mutagenesis |oclc=51445955}} 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). The half-life of EMS in 1M NaOH is 6 hours at room temperature, while in a 10% w/v sodium thiosulfate solution it has a half-life of 1.4 hours.

EMS is mutagenic, teratogenic, and carcinogenic {{cn|date=January 2025}}

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

{{Reflist}}

Category:Ethylating agents

Category:IARC Group 2B carcinogens

Category:Mutagens

Category:Teratogens

Category:Ethyl esters

Category:Mesylate esters