Environmental and Molecular Mutagenesis - Legacy Tobacco ...

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PROTAMINES IN GERM ZELL MUTAGENESIS, Gary A . Sega, Biology Division, ORNL, Oak
Ridge, TN 37831 .
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A number of chemicals are'powerful mutagens in late spermatids and early spermatozoa stages of the
mouse . Among these chemicals are ethyl methanesulfonate, methyl methanesulfonate, ethylene oxide,
and acrylamide . We have found that all four of these chemicals bind at much higher levels in the late
spermatids and early spermatozoa stages than in other stages . 11te increased binding in the sensitive
stages has been shown not to be the result of increased alkylation of DNA but rather to alkylation of the
protamine present in these stages . The sulfhydryl (-SH) groups present in the cysteine residues of
immature protamine in the sensitive stages are susceptible to aUcylation by these chemicals . We have
hypothesized that such alkylationVrevents nomsal disulfide bond formation in the protamine of the
developing sperm and leads to stresses that break the sperm chromatin, with resulting genetic damage to
the Fl progeny. Clearly, not all mutagenic chemicals act by the above mechanism, and other molecular
targets may be important in other germ-cell staps. However, our observations of how some chemicals
bind strongly to sperm protamine in mammals gives a new dimension to our understanding of mutational
processes in mammalian germ cells . [Research jointly sponsored by the Office of Health and
Environmental Research, U .S . DOE contract DE-ACOS-84OR21400 with Martin Marietta Energy
Systems, Inc ., and by the National Institute of Environmental Health Science under IAG No . 222Y01-
ES-10067 .]
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POTENTIAL ROLE OF GENOTOXICITY INDUCED BY GANMA IRRADIATION OF SPODOPTERA LITURA IN
ITS MANAGEMENT . S .S .Sehgal, and R .K .Seth, Department of Zoology, n ver y'8T-UEtihi,
Delhi-110007 (INDIA)
In accomplishing the laboratory evaluation of the biological effects of gamma irradiation
of a polyphagous lepidopteran pest, Spodoptern litura, it was observed that
as compared with other insects, Spodopteru required a very high dose (25,000 rad)
of gamma irradiation to produce a complete sterility . However, a gamma dose of 13,000
rad that induced a partial sterility (50%) in irradiated insects produced,progeny which
not only exhibited an increased sterility (ca .80%) but also a higher degree of sexual
competitiveness . The holokinetic nature of chromosomes could be a conceptual cytogenetic
explanation for these results . The fragments of irradiated holokinetic chromosomes
were probably represented in heterozyqous conditiorl in the offsprings, behaved as translocation
heterozygotes during meiosls in F-1 generafion which gave rise to aneuploid
gametes that caused dominant lethality in the next generation . The higher dose of gamma
irradiation caused some physiological effects like female infecundity, inability to
mate, reduced life span, malformations and sex-ratio skewed in favor of males . The
excess of males was probably caused by meiotic drive of maleness locus in this moth
and this phenomenon appears to have potential for the genetic control method for this
pest . Indeed, it is conceivable to identify and 'engineer' the deleterious genetic
mechanisms (or the genntoxicit .y)-induced by gamma irradiatinn, that might be transmitted
by the released moths to regulate the field population of this major pest in India .
515
MECHANISNS OF CAFFEINE INHIBITION OF DNA REPAIR IN E . COLI . Christopher P. Selby and
Aziz Sancar, Department of Biochemistry, University of North Carolina at Chapel Hill,
Chapel Hill, NC 27599 .
Caffeine inhibits excision repair and photoreactivation in E . coli in vivo . We
used purified E . coli enzymes and DNasel footprinting to study the mechanism of
inhibition . We do observe inhibition of ABC excinuclease and DNA photolyase by
caffeine in vitro . ABC excinuclease catalyses early events of excision repair :
recognition of damaged DNA and incision of the phosphodiester backbone on both sides
of the damage . The UvrA subunit is involved in damage recognition . Using an
oligonucleotide with a unique psoralen adduct, UvrA protects 33 base pairs
surrounding the adduct from DNaseI digestion . In the presence of caffeine, the
DNasel footprint of UvrA covers the entire oligonucleotide ; thus, caffeine promotes
the binding of UvrA to undamaged DNA . UvrA subunits "trapped" by caffeine would be
unable to catalyze repair . Photolyase binds to pyrimidine dimers, and upon
irradiation of the enzyme-dimer complex reverses the dimer . Using an oligonucleotide
with a unique thymine dimer, we found that caffeine binds specifically to the thymine
dimer and interferes with binding of photolyase to its substrate . Thus caffeine
inhibits the two repair systems in E . coli by entirely different mechanisms, by
promoting the nonspecific binding of the nucleotide excision repair enzyme and
interfering with specific binding of the photoreactivating enzyme . Supported by
grants from the NIH (GN32833) and NCI (5 T32 CA09156) .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts 177
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