Environmental and Molecular Mutagenesis - Legacy Tobacco ...

growth curve, instead peaking just before the cells entered log phase . Data from preUminary activation
studies using tobacco cells at diffeyent growth stages showed that lag-phase cells activated 2-aminofluorene
better than those in log or stationary phase . Although the maximum 2-aminofluorene activation coincided
with peak protein content, late log-phase cells were most competent in m-phenylenediamine activation,
suggesting that tobacco cells activate 2-aminofluorene and m-phcnylenediamine through different metabolic
pathways. Research funded in part by a WRC grant and USAF grant #88-AF-P-0511 .
548
THE POLY (ADP-RIBOSE) POLYMERASE GENE : DIRECT OR INDIRECT INVOLVSNIIirfP DJ DNA REPAIR AND
MAllONANCYI
Smulson, M .E .. Chemey, B ., Haque, J ., Huppi, C., Kang. V., Marr. K .. Mohrart . Z., Simpson. S ., and 8hatla, K .
Dept . of Biochemistry, Georgetown University School of Medicine, Washington, D .C .
Poly (ADP-ribose) polymerase Is a nuclear enzyme which appears to play a key role in modulating the
repair of damaged DNA mammalian calls . The catalytic activity of the purified enzyme is stringently
dependent upon the presence of strand breaks in DNA . The polymerase ls rapidly modulated In response to
mutagen treatment, probably representing one of the very early responses to DNA damage . We have evaluated
the role of endogenously and exogenously Induced DNA strand breaks on the transcriptional control of this
enzyme and also studied the expression of this gane during the eeU cycle as well as during differentiation,
both biological processes were endogenous discontinuous regions of DNA, and possibly strand breaks are
operative. Experiments using the polymerase cDNA In an expression vector indieate an Increased rate of
DNA repair In DNA damaged Cos cells, transiently transfeeted to overexpress the protein .
We have also mapped the human ehromowmtl location(s) of this gane . It has often been suggested that
cancer is associated with abnormal recombination events and mutations . We hypothesked that if any member
of the potymerase gene family or polymerase-related genes were necessary for reducing inappropriate
«combinationc, its loss might be associated with at least some human cancers. Tbe existence of a deletion
polymorphism in one of the polymerase genes, located on chromosome 13q32-ter, allowed us to test whether
deletion on both alleles on this gene correlates with inoreased tumor Incidence . There was a marked inereaso
(4x) in the frequency of the deleted allele in tumor DNA ; allelic loss was also noted. These results suggest
that deletions in the polymerase, or a gene linked close to it on chromosome 13 may operate to promote the
development of some types of cancer
. 'r
549 A
CHROMIUM(III) BINDS TO SINGLE-STRANDED DNA, INCREASES DNA POLYMERASE PROCESSIVITY,
AND INDUCES MUTAGENESIS IN E . COLI . E .T . Snow, L .S . Xu, and M .D . Cohent Institute of
Environmental Medicine, NYU Medical Center, P .O . Box 817, Tuxedo, NY (USA) .
Chromium is a suspected human carcinogen, but the mechanism of chromium-induced
carcinogenesis is unknown . Chromate ions are readily taken up by cells and are
reduced intracellularly via unstable Cr(V) and Cr(IV) intermediates to stable Cr(II1)
species . During this process DNA damage is produced and point mutations are induced
in many target genes . However, it is not known how Cr produces mutagenic damage or
if damage is produced indirectly by oxidative processes . Cr(III), the most stable
form of Cr, has been implicated in chromium toxicityt but, most Cr(III) species do not
cross cell membranes and are neither mutagenic nor carcinogenic in vivo . We have
investigated the genotoxicity of Cr(III) in vitro using a DNA replication assay and
in vivo by transfecting Cr(III)-treated DNA into competent E . coli and scoring for
survival and mutagenesis . Single-stranded (as) M13 DNA was treated with 1 to 10 yM
CrC13 (0 .5 - 24 hr, 370) and excess Cr removed by gel exclusion chromatography . The
DNA was primed with a 5'-32P-sequencing primer and primer extension was carried out
with DNA polymerase I(Klenow) or polymerase a-primase . Very low doses of Cr(III)
(1 t0 5 uM) increased the processivity of both polymerases although 10 uM Cr(III) was
inhibitory . When transfected into JM101 E . coli, Cr-treated es M13mp2 showed a dosedependent
increase in mutation frequency at the lac2„ gene . These results suggest
that Cr(III) alters the structure of the DNA template increasing the binding strength
of DNA polymerases and decreasing the fidelity of DNA replication . These
interactions may account, in part, for the mutagenicity of chromium ions in vivo .
550
A COMPARISON OF CHROMOSOME ABERRATION INDUCTION IN THE CHO AND CHL CELL
SYSTEMS BY 25 CHEMICALS . T . Sofuni, A . Matsuoka, M . Sawada, M . Ishidate
Jr ., and M . D . Shelby, National Institute of Hygienic Sciences,
Setagaya-ku, Tokyo (Japan), and National Institute of Environmental
Health Sciences, Research Triangle Park, NC (USA)
The present study was conducted to compare the results of chromosome
aberration tests using the CHL and CHO cell systems on 25 test chemi-
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts 189