Inactivation of phage T4 by ethylmethane sulfonate

A review of the genetic effects of ethyl methanesulfonate

Ethyl methanesulfonate (EMS) is a monofunctional ethylating agent that has been found to be mutagenic in a wide variety of genetic test systems from viruses to mammals. It has also been shown to be carcinogenic in mammals. Alkylation of cellular, nucleophilic sites by EMS occurs via a mixed SN1/SN2 reaction mechanism. While ethylation of DNA occurs principally at nitrogen positions in the bases, because of the partial SN1 character of the reaction, EMS is also able to produce significant levels of alkylation at oxygens such as the O6 of guanine and in the DNA phosphate groups. Genetic data obtained using microorganisms suggest that EMS may produce both GC to AT and AT to GC transition mutations. There is also some evidence that EMS can cause base-pair insertions or deletions as well as more extensive intragenic deletions. In higher organisms, there is clear-cut evidence that EMS is able to break chromosomes, although the mechanisms involved are not well understood. An often cited hypothesis is that DNA bases ethylated by EMS (mostly the N-7 position of guanine) gradually hydrolyze from the deoxyribose on the DNA backbone leaving behind an apurinic (or possibly an apyrimidinic) site that is unstable and can lead to single-strand breakage of the DNA. Data also exist that suggest that ethylation of some chromosomal proteins in mouse spermatids by EMS may be an important factor in causing chromosome breakage.

Recombinational repair of alkylation lesions in phage T4. II. Ethyl methanesulfonate

Treatment of bacteriophage T4 by ethyl methanesulfonate (EMS) caused more than a doubling in recombination between two rII markers. The functions of genes 47, 46, 32, 30, uvsX and y are known to be required for genetic recombination, and mutants defective in these genes were found to be more sensitive to inactivation by EMS than wild-type phage. This suggests that a recombinational pathway involving the products of these genes may be employed in repairing EMS induced lethal lesions. Genes 45 and denV are apparently not involved in recombination, and mutants defective in these genes were not EMS-sensitive. Gene 47, 46 and y mutants which were defective in the repair of EMS induced lethal lesions had no detectable deficiency in their ability to undergo EMS-induced mutation. This implies that recombinational repair of EMS lesions does not contribute substantially to EMS mutagenesis. The results obtained here with EMS are general similar to the results reported in the preceding paper with MNNG, suggesting that the lesions caused by both of these monofunctional alkylating agents may be eliminated by similar recombinational repair processes.

Inactivation of bacteriophage T4 by ethyl methanesulfonate: influence of host and viral genotypes

Inactivation of bacteriophage T4 by ethyl methanesulfonate (EMS) is a complex process which depends critically upon the conditions of treatment and upon both the viral and the host genotypes. EMS-inactivated particles are capable of multiplicity and cross-reactivation, indicating the need for caution in using EMS in certain types of mutation studies. The pyrimidine dimer excision systems of the phage and the host do not affect the EMS sensitivity of T4, but the T4x(+)y(+) system does. Mutational defects in the deoxyribonucleic acid (DNA) ligase and the DNA polymerase systems both of the virus and of its host also affect viral EMS sensitivity.

Inactivation of bacteriophage lambda containing semiconserved alkylated deoxyribonucleic acid

Immediate and delayed inactivation of ethylmethane sulfonate (EMS)-treated lambda phage were studied. Phage particles with one alkylated and one intact deoxyribonucleic acid (DNA) strand were obtained by allowing host-modified, EMS-treated phage to undergo one growth cycle in a nonmodifying host and selecting the progeny with semiconserved parental DNA on a restricting host. The results indicate that particles with one alkylated DNA strand are more sensitive to a second treatment with the alkylating agent. When incubated at 37 C, they are subject to inactivation at a rate which is smaller than that of phages containing two alkylated DNA strands. It appears that depurination events in one of the DNA strands of a phage particle are sufficient to cause death.