Environmental and Molecular Mutagenesis - Legacy Tobacco ...

8 1989 EMS Abstracts
Notes led to the hypothesis that proliferating rather then "resting" T-lyaphocytes are
preferentially susceptible to gsne mutations in vivo . This may have significant
implications for interpreting human in vivo mutagenicity studies . Research supported by
NCI CA30688 and DOE FG0287ER60502 .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
INFLUENCE OF DIFFERENT FACTORS ON THE INDUCTION or KALSEGREGATION IN
SACCHAROMYCES CEREVISIAE D61 .M BY BAVISTAN .
Silvio Albertini, Pharmaceutical Research, Department of Toxicology,
F .Hoffmann-La Roche o Co ., Ltd, CH-4002 Basel, Switzerland .
Bavistan is known as a potent inducer of malsegregation in Sacharom ces
cerevisiae . with both standard protocols used with S . cerev s ae D .M
overnight incubation and cold treatment protocol, respectively)
bavistan induced malsegregants in the same range . The frequencies obtained
were not influenced by the plating volume used on selective medium
. The higher the YEP content the more distinct the toxicity and the
induction of malsegregants was . The physiological temperature for
yeasts of 28°C led to a more pronounced induction than 33°C and 37°C . A
clear observable induction by bavistan was detectable after 8 hours
incubation (overnight protocol) and 1 .5 hours of the second incubation
period (cold treatment protocol), respectively .
Comparison of the growth of mixed cultures of red, cycloheximide
sensitive cells and white, cycloheximide resistant, leucine auxotrophic
cells prepared at different ratios revealed, that there is a strong
selection towards red cells and against the malsegregants .
PLASKID COPY NUMBER AND MUTANT FREQUENCIES IN S .TYPHIMURIUM TA102
Silvio Albertini and Elmar Gocke, Pharmaceutical Research, Department
o Tox co ogy, c .Hoffmann-La Roche i Co . Ltd, CH-4002 Basel,Switserland .
Tetracycline and chloramphenicol increase the number of mutant colonies
of strain TA102, which carries the reverting gene on the plasmid pAQl .
Determination of the plasmid content by agarose gel analysis shows that
the increase of the mutant colony number is paralleled closely by an
increase of the number of pAQl plasmids per cell, indicating that the
two compounds do not increase the frequency of mutants "per gene", but
only enhance the number of genes at which mutations can occur . Thus,
not considering the molecular processes could result in mistakenly
attributing the increase in the number of mutants per plate (respective
to the number of mutants per cell) to a mutagenic activity of the antibiotics
. An other antibiotic, kanamycin, acts by reducing the translation
fidelity which leads to read through of the ochre stop codon and
thereby to an accumulation of enough functional enzyme so that enhanced
cellular growth is possible .
These different mechanisms all mimic mutagenic responses with some
analogies to the effect of growth enhancing compounds (e .g . complex
mixtures containing histidine) . It is discussed whether such false
positive results are likely to occur in routine testing with TA102 and
how to avoid possible misinterpretation .
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INDIRECT EFFECT OF SOME DNA DAMAGING AGENTS ON LAMBDA RECOMBINATION . D . Alcintara-Dfaz
and N . Brefia-Valle, Instituto Nacional de lnvsstigaciones Nucleares, Kixico, D .F . (NE-
IQCO) .
Recombinant progeny of undamaged lambda phage, increases up to four times when infecting
E . coli hosts previously irradiated with UV light. A similar effect occurs in
the mutant recA-441 (tif-1) SOS induced by hest, but so far none could be detected in
lexA (ind-) bacteria (Alcfintara and BreBa, data submitted for publicatioa) . All these
results suggeat an SOS-dependent stimulation of undamaged lambda recombination . The
present work shows more data supporting the former view . Phage crosses were carried
out according to standard procedures in hosts with distinct repair capabilities treated
with either UV or three other genotoxicants . An increase of 7 times the normal recombinant
progeny was found in umuC cells exposed to 50 J/m2 of W light, a fact which
to our view proves that these ara true recombinants and not mutants due to the well
known W effect . On the other hand the experiments using FRlC, l04S and MJNG as recombina
tion stimulants show that whereas no affect could be found in treated E . coli lexA
(ind-) hosts, a significant increase in phage recombinaits occurred whan Tnfecting
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