Environmental and Molecular Mutagenesis - Legacy Tobacco ...

104 1989 EMS Abstracts
Notes CARCINOGENESIS OF FOODS . lb Knudsen, DVM, Institute of Toxicology,
National Food Agency, Msrkhmj Bygade 19 . DK 2860 Smborg (Cph .),
Denmark .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
Food is a major determinant of human health and disease, not only from
a nutritional point of view, but also from a toxicological point of view .
Thus food toxicology is not only a scientific discipline to deal with the
toxicology of food additives but also a ma jor source of knowledge about
impact of major and minor food constituents on human health . The
Institute of Toxicology has established a testing programme to deal with
these matters covering natural fibers in the protection against colon
cancer, possible interaction between urethane and alcohol in carcinogenesis,
food mutagens as a human health factor . The paper will discuss
our recent progress within these areas of research .
INDUCTION OF CHROMOSOME CHANGES BY METAL COMPOUNDS
IN CULTURED CHO CELLS .
TS. Kochhar, B . Leonard, K . Harris, W . Moody
Kentucky State University, Frankfort, KY 40601
Several metal compounds have been identified as potential carcinogens through
occupational exposure as well as in the laboratory . Since chromosome changes such as
abberations and sister-chromatid exchange have been linked to DNA damage, the
influence of certain metal salts on these parameters was assessed in cultured CHO cells .
The cells were treated with CdCI2, Cr0„ HgCI= and N1CIz for 24 h . The concentrations
used for aberration assay were 10'7 -10" M and for SCE assay it was 10-s-10's M . It
was observed that all compounds enhanced . various types of chromosomal abnormalities
compared to the controls . CdCl2 seemed to have the maximum effect as the cultures
treated with 10-7 and 10-s M of this compound revealed a considerable number of
chromosomes with two or more centromeres . Other increase in abnormalities were the
ring chromosomes, chromatid breaks, chromatid exchanges and the stickiness of the
chromosomes . CdCI„ Cr03 and NIC1 also enhanced SCE frequencies . In higher
concontrations of these compounds (10'~ and 10-s M) SCE/cell Incrpsed more than twofold
compared to the BrdU controls . HsCI= was relatively ineffective in raising the SCE
rates . These studies indicate a definite link between the metals and the mammalian
chromosomep-which calls for further detailed studiq . (5upported by NIH-MgRS RR
08124 grant .)
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DNA SEQUENCE ANALYSIS OF MUTATIONS INDUCED IN YEAST BY EXCESS THYMIDYLATE : EVIDENCE
FOR NEXT•NUCLEOTIDE EFFECTS . S .E . Kohalmi and B .A . Kunz, Microbiology Department, The
University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
In thymidylate (dTNP) auxotrophs of the yeast Saccharomvcas cerevisiaa, intracellular
dTTP levels can be modulated by varying the concentration of dTMP in the growth
medium . Provision of excess dTMP is mutagenic in yeast . Recently, yeast DNA polymerase
III was found to have a 3' -> 5' exonuclease activity capable of proofreading in
vitro . Thus, mutations induced by excess dTMP could be due to misincorporation of the
nucleotide and the misincorporation frequency might be enhanced by next-nucleotide
effects reducing the efficacy of the 3' -> 5' proofreading activity . On this basis,
and since dTTP is a positive effector of GDP reduction In yeast, excess dTMP would be
expected to cause increases in substitution by T and in the proportion of events at
sites flanked by a 3' T or C . To test these possibilities, we are using DNA sequence
analysis of mutations induced by excess dTMP in the SUP4-o gene of yeast . To date .
100 induced mutations have been characterized and the spectrum and distribution of
changes have been compared to those for 306 spontaneous mutations . We have determined
that : 1 . 86% of the induced substitutions involve replacement by T whereas only 64%
of the spontaneous changes do ; 2 . approximately 90% of the induced mutations occur
at sites with a 3' flanking T or G vs . 73% for the spontaneous mutations . The results
argue that dTMP misincorporation is responsible for the induced mutations and suggest
that a proofreading function is part of the yeast DNA replication complex In vivo .
Currently, we are analyzing additional mutants . (Supported by NSERC Canada)
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THE USE OF LAbIDDA PHAGE SHUTTLE VECTORS IN TRANSGENIC MICE FOR
DEVELOPMENT OF A SHORT TERM MUTAGENICITY ASSAY
Kohler, S .W ., Provost, G .S ., Kretz, P .L ., Sorge, J ., Huse, W .D . and
Short . J .M . Stratagene, 11099 North Torrey Pines Road, La Jolla, CA
92037 .
A short term mutagenesis assay has been developed which will permit
analysis of suspected genotoxic substances in whole animals .
Transgenic mice containing a stably integrated bacteriophage lambda
shuttle vector can be rescued at high efficiency (>1000 pfu/µg of
genomic DNA/integrated copy) from isolated genomic DNA with In vitro
lambda packaging extracts . This rescue efficiency allows the recovery
of over one million lambda phage genomes per tissue, a level
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