Ref for EMS reaxn

Satoshi NAITO naito at
Mon Nov 11 01:21:25 EST 2002

Dear Friends,

About half a year (!) ago, I posted the following request for information:
>  EMS usually causes a G to A mutation. Do anyone know a reference for this
>  reaction, or a paper clearly stating this?

I received several good responses.  Thank you very much Jim Tokuhisa, Ben
Holt, Anne Britt, Susanne Kohalmi, and Remko Offringa (thanx for a nice
figure).  While I was trying to obtain some of the references, I forgot to
send this feedback. (-_-;)

As a chemical reaction, the most major product on double stranded DNA from
EMS treatment is N-7 ethyl G.  HOWEVER, to produce a genetic mutation, the
modified base has to go thru a series of repairs, and the one that
contributes best to produce a mutation is O-6 ethyl G, which pairs with both
C and T.  References are listed at the bottom of this mail.

Interestingly, in the case of fruitfly, G to A change is not a major outcome
of EMS mutagenesis, perhaps because flies are usually treated with EMS as a

Given that EMS produces only G to A (C to T, in the reverse strand)
mutations, many of the base changes in amino acid codons will be silent:
Lys (AAA/AAG), Tyr (UAU/UAC), Asn (AAu/AAC), Phe (UUU/UUC), Ile
(AUU/AUC/AUA), and STOPs (UAA/UAG/UGA).  It's a pity that those active amino
acids like Lys and Tyr are inert to EMS mutagenesis.

Many others also make only conservative changes:
i) Arg (AGA/AGG) can only be mutated to Lys.
ii) Glu (GAG) can only be mutated to Asp.
iii) 4 of the 6 Leu codons are inert for EMS mutagenesis, and for the
remaining 2 (CUU/CUC), only a conservative change of Leu to Phe can be
iv) 3 of the 4 Val codons make conservative change to Ile, the other can
change to Met.
v) 2 of the 3 Asp codons can change to Asn, the other to Lys.
etc, etc...

There is a report in yeast that while EMS is selective to G to A changes,
methyl methanesulfonate showed no selectivity (Prakash and Sherman, JMB, 79:
65-82, 1973).

The references for EMS raction/EMS-induced mutations are:

Sega, G. A. (1984). A review of the genetic effects of ethyl
methanesulfonate. Mutation Res 134, 113-142.

Friedberg "DNA Repair and Mutagenesis" ASM Press.

in yeast:
S. E. Kohalmi and B. A. Kunz. Role of neighbouring bases and assessment of
strand specificity in ethylmethanesulphonate and
N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis in the SUP4-o gene of
Saccharomyces cerevisiae. J.Mol.Biol. 204:561-568, 1988.

in E. coli
P. A. Burns, F. L. Allen, and B. W. Glickman. DNA sequence analysis of
mutagenicity and site specificity of ethyl methanesulfonate in UvrB-
strains of Escherichia coli. Genetics 113:811-819, 1986.

M. Pienkowska, B. W. Glickman, A. Ferreira, M. Anderson, and M. Zielenska.
Large-Scale mutational analysis of EMS-induced mutation in the lacI gene of
Escherichia coli. Mutat.Res. 288:123-131, 1993.

  Satoshi Naito
  Division of Applied Bioscience
  Graduate School of Agriculture, Hokkaido University
  Sapporo 060-8589, JAPAN
  Phone: +81-11-706-2800
  FAX: +81-11-706-4932
  e-mail: naito at


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