Spectra of spontaneous frameshift mutations at the hisD3052 allele of Salmonella typhimurium in four DNA repair backgrounds.

To characterize the hisD3052 -1 frameshift allele of Salmonella typhimurium, we analyzed approximately 6000 spontaneous revertants (rev) for a 2-base deletion hotspot within the sequence (CG)4, and we sequenced approximately 500 nonhotspot rev. The reversion target is a minimum of 76 bases (nucleotides 843-918) that code for amino acids within a nonconserved region of the histidinol dehydrogenase protein. Only 0.4-3.9% were true rev. Of the following classes, 182 unique second-site mutations were identified: hotspot, complex frameshifts requiring DeltauvrB + pKM101 (TA98-specific) or not (concerted), 1-base insertions, duplications, and nonhotspot deletions. The percentages of hotspot mutations were 13.8% in TA1978 (wild type), 24.5% in UTH8413 (pKM101), 31.6% in TA1538 (DeltauvrB), and 41.0% in TA98 (DeltauvrB, pKM101). The DeltauvrB allele decreased by three times the mutant frequency (MF, rev/10(8) survivors) of duplications and increased by about two times the MF of deletions. Separately, the DeltauvrB allele or pKM101 plasmid increased by two to three times the MF of hotspot mutations; combined, they increased this MF by five times. The percentage of 1-base insertions was not influenced by either DeltauvrB or pKM101. Hotspot deletions and TA98-specific complex frameshifts are inducible by some mutagens; concerted complex frameshifts and 1-base insertions are not; and there is little evidence for mutagen-induced duplications and nonhotspot deletions. Except for the base substitutions in TA98-specific complex frameshifts, all spontaneous mutations of the hisD3052 allele are likely templated. The mechanisms may involve (1) the potential of direct and inverted repeats to undergo slippage and misalignment and to form quasi-palindromes and (2) the interaction of these sequences with DNA replication and repair proteins.

The glutathione S-transferase M1 (GSTM1) null genotype and benzidine-associated bladder cancer, urine mutagenicity, and exfoliated urothelial cell DNA adducts.

Multiple studies in the general population have suggested that subjects with the glutathione S-transferase M1 (GSTM1)-null genotype, who lack functional GSTM1, are at higher risk for bladder cancer. To evaluate the impact of the GSTM1-null genotype on bladder cancer caused by occupational exposure to benzidine and to determine its influence on benzidine metabolism, we carried out three complementary investigations: a case-control study of bladder cancer among workers previously exposed to benzidine in China, a cross-sectional study of urothelial cell DNA adducts and urinary mutagenicity in workers currently exposed to benzidine in India, and a laboratory study of the ability of human GSTM1 to conjugate benzidine and its known metabolites in vitro. There was no overall increase in bladder cancer risk for the GSTM1-null genotype among 38 bladder cancer cases and 43 controls (odds ratio, 1.0; 95% confidence interval, 0.4-2.7), although there was some indication that highly exposed workers with the GSTM1-null genotype were at greater risk of bladder cancer compared to similarly exposed workers without this allele. However, the GSTM1 genotype had no impact on urothelial cell DNA adduct and urinary mutagenicity levels in workers currently exposed to benzidine. Furthermore, human GSTM1 did not conjugate benzidine or its metabolites. These results led us to conclude that the GSTM1-null genotype does not have an impact on bladder cancer caused by benzidine, providing a contrast to its association with elevated bladder cancer risk in the general population.

Effects of television on metabolic rate: potential implications for childhood obesity.

The effects of television viewing on resting energy expenditure (metabolic rate) in obese and normal-weight children were studied in a laboratory setting. Subjects were 15 obese children and 16 normal-weight children whose ages ranged from 8 to 12 years. All subjects had two measured of resting energy expenditure obtained while at rest and one measurement of energy expenditure taken while viewing television. Results indicated that metabolic rate during television viewing was significantly lower (mean decrease of 211 kcal extrapolated to a day) than during rest. Obese children tended to have a larger decrease, although this difference was not statistically significant (262 kcal/d vs 167 kcal/d, respectively). It was concluded that television viewing has a fairly profound lowering effect of metabolic rate and may be a mechanism for the relationship between obesity and amount of television viewing.

A longitudinal analysis of accelerated weight gain in preschool children.

The purpose of the current investigation was to determine the dietary, physical activity, family history, and demographic predictors of relative weight change in a cohort of 146 children over a 3-year period. Results indicated that boys of normal-weight parents or who had only one parent overweight showed decreases in their body mass index (BMI) while those with two parents overweight showed increases. Girls with an overweight father showed BMI increases while others experienced decreases in BMI. Additionally, baseline intake of kilocalories from fat as well as decreases in fat intake were related to decreases in BMI. At higher levels of baseline aerobic activity, subsequent changes in BMI decreased. There was also a trend for changes in leisure activity--increases in children's leisure activity was associated with decreases in subsequent weight gain. Modifiable variables (ie, dietary intake, physical activity) accounted for more of the variance in changes in child BMI change than nonmodifiable variables (eg, number of parents obese). These results strongly suggest that encouragement of heart healthy dietary intake patterns and participation in physical activity can decrease accelerated weight gain and obesity, even in preschool children.

Molecular analysis of mutations induced at the hisD3052 allele of Salmonella by single chemicals and complex mixtures.

More single chemicals and complex environmental mixtures have been evaluated for mutagenicity at the hisD3052 allele of Salmonella, primarily in strain TA98, than in any other mutation assay. The development of colony probe hybridization procedures and the application of the polymerase chain reaction and direct DNA sequencing has permitted rapid molecular access to this allele. We discuss these techniques and the resulting mutation spectra that have been induced by a variety of environmental mutagens and complex mixtures. A common GC or CG deletion within a hot-spot region of the sequence dominates most of the spectra. In addition to this two-base deletion, we have recovered about 200 other types of mutations within the 72-base target for reversion of the hisD3052 allele. These include a variety of deletions (as large as 35 bases), duplications (as large as 46 bases), and complex mutations involving base substitutions. The quasipalindromic nature of the target sequence and its potential to form DNA secondary structures and slippage mismatches appear to be an important basis for the mutability of this allele.

Effects of phenylpropanolamine on withdrawal symptoms.

A prior report (Klesges et al. 1990) suggested that phenylpropanolamine (PPA) was successful in reducing the smoking withdrawal symptom of weight gain in a sample of women. The current investigation evaluates whether the effects of phenylpropanolamine (PPA; up to 10/day PPA gums) on withdrawal symptoms associated with smoking cessation are specific to weight and weight-related symptoms or whether PPA alleviates withdrawal in general. One hundred and seven adult smokers (56 men, 51 women) were randomly assigned, in this double-blind trial, to chew either 8.33 mg phenylpropanolamine gum or a placebo gum. Subjects were then aided to quit smoking for 4 weeks. PPA did not enhance cessation rates. Results from the 47 subjects who successfully quit smoking indicated that postcessation weight gain and ratings of hunger were significantly reduced in both men and women for those assigned to the PPA group relative to the placebo group. Overall, no effects of PPA relative to placebo were observed for other smoking-related withdrawal symptoms. Thus, although PPA appears to reduce weight gain and alleviate weight-related symptoms, no effects on other withdrawal symptoms were observed. Future research directions are suggested.

Subtrochanteric fractures of the femur.

Subtrochanteric fractures of the femur comprise only 5% to 7% of hip fractures, but are important because of the difficulty in management. They combine the problem of instability to varus deformation common to comminuted intertrochanteric fractures and the problem of delayed union common to diaphysial fractures of the femur. While the benefits of open reduction and internal fixation in decreasing morbidity and mortality have been well established, formidable operative complications have occurred when this fracture is treated like an intertrochanteric fracture. Improved results have been obtained by utilizing a fixation device that can control the intertrochanteric instability and that has sufficient strength to withstand deforming forces that may be present for up to a year while the fracture is uniting. Bone grafting has been found very useful in shortening the overall period of healing.

Mutation spectra of Glu-P-1 in Salmonella: induction of hotspot frameshifts and site-specific base substitutions.

We used colony probe hybridization and PCR/DNA sequence analysis to determine the mutations in approximately 1,640 revertants of the -1 frameshift allele hisD3052 and approximately 260 revertants of the base substitution allele hisG46 of Salmonella typhimurium induced by the heterocyclic amine cooked food mutagen 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1). All of the mutations were at sites containing guanine, which is the base at which Glu-P-1 forms DNA adducts. A hotspot mutation involving the deletion of a CG or GC within the sequence CGCGCGCG accounted for 100% of the Glu-P-1-induced mutations at the frameshift allele in strains TA1978 (uvr+) and TA1538 (delta uvrB) and 99% in TA98 (delta uvrB, pKM101). To explain the induction of these hotspot mutations by Glu-P-1, we describe here a more detailed version of our recently proposed correct incorporation/slippage model [Genetics:136:731, 1994]. We propose that after cytosine is incorporated correctly opposite a Glu-P-1-adducted guanine, various slipped intermediates may form (a total of 18), depending on which guanine is adducted and whether it remains within the helix or becomes extrahelical. This variety of mutational pathways may account for the high mutability of the hotspot sequence by Glu-P-1. Although the pKM101 plasmid does not influence the mutagenic potency or mutational spectrum of Glu-P-1 at the frameshift allele, it is required by Glu-P-1 to revert the base substitution allele, where Glu-P-1 induces G-C --> T-A transversions (75%) and G-C --> tA-T transitions (25%) exclusively at a single site (the second position of the CCC codon of the hisG46 allele). The limited (20-30 times less) base substitution mutagenic potency of Glu-P-1 relative to its frameshift mutagenic potency as well as the extreme site specificity exhibited by Glu-P-1 for base substitutions may have bearing on the lack of base substitutions identified in ras genes in Glu-P-1-induced rat colon tumors.

Mutation spectra in Salmonella of complex mixtures: comparison of urban air to benzo[a]pyrene.

We used an ion-exchange procedure coupled to the Salmonella assay to fractionate the dichloromethane-extractable particulate organics from an urban air sample collected in Boise, Idaho. A resulting base/neutral fraction contained 81% of the mutagenic activity but only 36% of the mass of the unfractionated sample. Chemical analysis showed that polycyclic aromatic hydrocarbons (PAHs) accounted for much of the mutagenic activity of the air sample. Colony probe hybridization, PCR, and DNA sequence analysis were then used to determine the mutations induced by the complex mixtures and a model PAH, benzo[a]pyrene (BAP) in approximately 900 revertants of the frameshift hisD3052 allele and approximately 400 revertants of the base-substitution hisG46 allele. The majority (93-94%) of the mutations induced at the frameshift allele in strain TA98 by the whole or base/neutral fraction of the urban air sample was a hotspot 2-base deletion of a CG or GC within the sequence CGCGCGCG. The remaining mutations were complex frameshifts that consisted of -2 or +1 frameshifts associated with a flanking base substitution. BAP induced a somewhat similar pattern of mutations, with 70% being the hotspot mutation, 23% being complex frameshifts, and the remaining being deletions. The inferred base-substitution specificity associated with the complex frameshifts at the hisD3052 allele (primarily G.C-->T.A transversions) was consistent with the observation that this same transversion was the primary mutation induced by the whole urban air sample and BAP at the base-substitution allele in strain TA100. At the frameshift allele, adducts that promote correct incorporation/slippage could account for hotspot mutations, whereas those that promote misincorporation/slippage could account for complex frameshifts. At the base-substitution allele, a mixture of adducts or of adducts with multiple conformations could account for the observed proportion of transitions and transversions. Combined with the bioassay-directed chemical analysis, these results from the first mutation spectra of a complex mixture suggest that such spectra reflect the dominance of particular classes of chemical mutagens within the mixture.

Mutation spectra in salmonella of chlorinated, chloraminated, or ozonated drinking water extracts: comparison to MX.

Drinking water samples were prepared in a pilot-scale treatment plant by chlorination (Cl2), chloramination (NH2Cl), ozonation (O3), or O3 followed by Cl2 or NH2Cl; and the nonvolatile acidic organics of the raw and treated waters were extracted by XAD/ethyl acetate and evaluated for mutagenicity in Salmonella (-S9). The extracts were 2-8 times more mutagenic in TA100 than in TA98, and the mutagenic potencies of the water extracts ranked similarly in both strains: Cl2 > O3 + Cl2 > NH2Cl > O3 + NH2Cl > O3 > raw. 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), which was estimated to account for approximately 20% of the mutagenic activity of the extracts, was shown to be the most potent compound tested thus far in a prophage-induction assay in Escherichia coli and a forward-mutation assay in Salmonella TM677. The mutations in approximately 2,000 revertants of TA98 and TA100 induced by MX and the water extracts were analyzed by colony probe hybridization and polymerase chain reaction/DNA sequence analysis. The water extracts and MX produced similar mutation spectra, which consisted in TA100 of predominantly of GC-->TA transversions in the second position of the CCC (or GGG) target of the hisG46 allele. This spectrum resembles that produced by large aromatic compounds and is distinct from that produced by alkylating agents and the semivolatile drinking water mutagen dichloroacetic acid. In TA98, MX and those water extracts resulting from the introduction of the chlorine atom produced 50-70% hotspot 2-base deletions and 30-50% complex frameshifts (frameshifts with an adjacent base substitution--mostly GC-->TA transversions as found in TA100). No other compound or mixture is known to induce such high frequencies of complex frameshifts. These results suggest that MX and "MX-like" compounds (possibly halogenated aromatics, such as halogenated polycyclic aromatic hydrocarbons) account for much of the mutagenic activity and specificity of the nonvolatile organics in drinking water and that these halogenated organics are especially capable of promoting misincorporation by the DNA replication complex. This study provides further evidence that the mutation spectrum of a complex mixture reflects the dominance of one or a few classes of chemical mutagens within the mixture.

Glutathione S-transferase-mediated induction of GC-->AT transitions by halomethanes in Salmonella.

Halomethanes are among the most common mutagenic and carcinogenic disinfection by-products present in the volatile/semivolatile fraction of chlorinated drinking water. Recent studies have demonstrated that the mutagenicity of dichloromethane (CH2Cl2) and bromodichloromethane (BrCHCl2) can be mediated by a theta-class glutathione S-transferase (GSTT1-1). These studies used strain RSJ100 of Salmonella, which is a derivative of the base-substitution strain TA1535 (hisG46, rfa, delta uvrB), into which has been cloned the GSTT1-1 gene from rat. In the present report, we have extended these studies by demonstrating that the mutagenicity of two additional brominated trihalomethanes, bromoform (CHBr3) and chlorodibromomethane (CICHBr2), are also mediated by GSTT1-1 in RSJ100. Using a Tedlar bag vaporization technique, the mutagenic potencies (revertants/ppm) for these two compounds as well as the compounds tested previously rank as follows: CHBr3 approximately CICHBr2 > BrCHCl2 approximately CH2Cl2. To explore the mutational mechanism, we determined the mutation spectra of all four halomethanes at the hisG46 allele by performing colony probe hybridizations of approximately 100 revertants induced by each compound. The majority (96-100%) of the mutations were GC-->AT transitions, and 87-100% of these were at the second position of the CCC/GGG target. In contrast, only 15% of mutants induced by CH2Cl2 were GC-->AT transitions in the absence of the GSTT1-1 gene in strain TA100 (a homologue of TA1535 containing the plasmid pKM101). The ability of GSTT1-1 to mediate the mutagenicity of these di- and trihalomethanes and the induction of almost exclusively GC-->AT transitions by these compounds suggest that these halomethanes are activated by similar pathways in RSJ100, possibly through similar reactive intermediates. The implications of these findings are discussed in relation to previous experimental work on the GST-mediated bioactivation of dihalomethanes, which includes the possible formation of GSH intermediates and/or GSH-DNA adducts.

Mutagenicity and mutation spectra of 2-acetylaminofluorene at frameshift and base-substitution alleles in four DNA repair backgrounds of Salmonella.

We used colony probe hybridization procedures to determine the mutations in approximately 600 revertants of the -1 frameshift allele hisD3052 and approximately 200 revertants of the base-substitution allele hisG46 of Salmonella typhimurium induced by 2-acetylaminofluorene (2-AAF) in the presence of Aroclor-induced rat liver S9. 2-AAF was primarily a frameshift mutagen, exhibiting 5 times more frameshift than base-substitution activity. The only frameshift mutation 2-AAF induced at the hisD3052 allele was a hotspot (-2) deletion within the sequence CGCGCGCG. The addition of the pKM101 plasmid had a small effect on the mutagenic potency of 2-AAF at this allele in a uvr+ background and no effect on the mutation spectra in either a uvr+ or uvr- background. The small amount of base-substitution activity exhibited by 2-AAF at the hisG46 allele required the presence of both the pKM101 plasmid and the uvrB mutation. The base substitutions were G.C-->T.A transversions (86%) and G.C-->A.T transitions (14%), and 85% of the substitutions were at the second position of the CCC target of the hisG46 allele; the remainder were at the first position. We propose that the hotspot frameshift may be initiated by N-acetyl-2-aminofluorene adducts located at the C(8) position of any of the guanines except the first one in the CGCGCGCG hotspot sequence. The mutation might then result from correct incorporation of cytosine opposite the adducted guanine, followed by a 2-base slippage according to our recently proposed correct-incorporation/slippage model. The hotspot mutation may also result from a 2-AAF-induced B- to Z-DNA transition at the repeating GpC site as well as by the action of enzymes involved in DNA metabolism, such as DNA resolvases or topoisomerases, on DNA structures that have been distorted by 2-AAF adducts. The small amount of 2-AAF-induced base-substitution activity may be due to mispairing of adenine opposite the minor aminofluorene adduct at the C(8) position of guanine.

Mutation spectrum of a binary mixture of mutagens (methapyrilene and sodium azide) in strain TA1535 of Salmonella.

Methapyrilene (MP) is a rat-liver carcinogen and cocarcinogen that exhibits a narrow spectrum of mutagenic activity in Salmonella typhimurium, inducing only a 2-fold increase in revertants only in the base-substitution strain TA1535; it also enhances the mutagenic activity of sodium azide (NaN3) in the same strain. To examine the effects of MP at the molecular level, we used the colony probe hybridization procedure developed by Cebula and Koch (Mutation Res., 229 (1990) 79-87) to identify the base substitutions in approximately 800 background, MP-, NaN3-, and MP + NaN3-induced revertants of the hisG46 allele of strain TA1535. The predominant mutation in all 4 mutation spectra was a CCC-->CTC transition. The results suggest a mechanism by which MP enhances the infidelity of the DNA replication complex or inhibits a DNA repair or proofreading function, resulting in the production of more of the same error that occurs normally and that is also induced by NaN3. Such a mechanism might be the basis for the carcinogenic and cocarcinogenic activities of MP. To our knowledge, this is the first report of the molecular analysis of mutants produced by exposure of cells to a binary mixture of mutagens.

Mutation spectra of chemical fractions of a complex mixture: role of nitroarenes in the mutagenic specificity of municipal waste incinerator emissions.

Using an ion-exchange procedure coupled to a microsuspension Salmonella assay, we fractionated the dichloromethane-extractable particulate organics emitted by a municipal waste incinerator. Most (80-95%) of the mutagenic activity resided in the neutral/base fraction; however, the polar neutral fraction accounted for 12% of the direct-acting mutagenic activity. The mutagenic potencies of the whole extract and the various fractions were 4-15 times greater in the absence than in the presence of S9. Results with strains deficient in classical nitroreductase (TA98NR) and transacetylase (TA98/1,8-DNP6) indicated that a majority of the direct-acting mutagenicity was due to nitroarenes. This was confirmed by bioassay-directed subfractionation of the neutral/base faction by a cyanopropyl/HPLC method. The mutations in -3,000 revertants (approximately 400 each induced in TA98 by the whole extract, the neutral/base and polar neutral fractions from the ion-exchange column and 3 of the neural/base subfractions from the HPLC column; along with 200 revertants each induced by the model nitroarene 1-nitropyrene (1NP) in strains TA98, TA1538 and TA100) were analyzed by probe hybridization and PCR/DNA sequence analysis. The results indicated that nitroarenes such as 1NP that eluted in the neutral/base fraction accounted for at least 50% of the direct-acting mutagenicity and induced only a hotspot 2-base deletion in the sequence (CG)4 in TA98. In contrast, most of the complex frameshifts (a frameshift with a flanking base substitution) induced by the whole extract were induced by nitroarenes other than 1NP that were activated by transacetylation and that eluted in the polar neutral fraction. This study (1) identifies nitroarenes as an important contributor to the mutagenic activity of the emissions from municipal waste incinerators; (2) confirms our previous conclusion that the mutation spectrum of a complex mixture reflects the dominance of particular classes of chemical mutagens within the mixture; and (3) demonstrates the possibility of isolating certain chemical fractions of a complex mixture that induce certain classes of mutations produced by the whole, unfractionated mixture.

Mutation spectra in Salmonella of sunlight, white fluorescent light, and light from tanning salon beds: induction of tandem mutations and role of DNA repair.

We evaluated the mutagenicity of sunlight (SUN), uncovered coolwhite fluorescent light (FLR), and light from a tanning salon bed (TAN) at the base-substitution allele hisG46 of Salmonella in four DNA repair backgrounds (wild type, uvrB, pKM101, and uvrB + pKM101). Approximately 80% of the radiation emitted by TAN was within the ultraviolet (UV) range, whereas only approximately 10% of the SUN and approximately 1% of the FLR radiation was UV. TAN emitted similar amounts of UVA and UVB, whereas SUN emitted 50-60x and FLR emitted 5-10x more UVA relative to UVB. Based on total dose (UV + visible), the mutagenic potency ranking was TAN > FLR > SUN. Using colony probe hybridization and PCR/DNA sequence analysis, approximately 3000 revertants were analyzed to determine the mutational specificity of the three light sources. The mutation spectra and those induced by 254-nm UV had common features. The uvrB mutation enhanced the mutagenicity of the environmental UV sources more (20-216x) than did the pKM101 plasmid (approximately 20x) relative to wild type DNA repair. All light sources induced equal proportions of transitions and transversions in excision repair-proficient strains, but they induced more transitions relative to transversions in uvrB-containing strains. The majority of the mutations were G.C-->A.T transitions that were induced equally frequently at the first or second position of the CCC codon of the hisG46 allele in all strains except TA1535 (uvrB), where SUN and FLR induced transitions preferentially at the first position, and TAN induced them preferentially at the second position. Identified or presumptive multiple mutations, which constituted the only mutational class enhanced by all three light sources in the presence of uvrB and pKM101 either alone or together, accounted for 3-5% of the induced mutations in the plasmid-containing strains, and their increases (38-82-fold) in TA100 (uvrB, pKM101) were the highest of any mutational class. Of the TAN-induced multiple mutations, 83% (19/23) were CC-->TT tandem transitions. These results show that exposures to the nonsolar environmental UV sources FLR and TAN produce mutations similar to those produced by SUN, a known carcinogen.

Mutagenicity in lung of big Blue((R)) mice and induction of tandem-base substitutions in Salmonella by the air pollutant peroxyacetyl nitrate (PAN): predicted formation of intrastrand cross-links.

Peroxyacetyl nitrate (PAN) is a ubiquitous air pollutant formed from NO(2) reacting with acetoxy radicals generated from ambient aldehydes in the presence of sunlight and ozone. It contributes to eye irritation associated with photochemical smog and is present in most urban air. PAN was generated in a chamber containing open petri dishes of Salmonella TA100 (gas-phase exposure). After subtraction of the background mutation spectrum, the spectrum of PAN-induced mutants selected at 3.1-fold above the background mutant yield was 59% GC-->TA, 29% GC-->AT, 2% GC-->CG, and 10% multiple mutations - primarily GG-->TT tandem-base substitutions. Using computational molecular modeling methods, a mechanism was developed for producing this unusual tandem-base substitution. The mechanism depends on the protonation of PAN near the polyanionic DNA to release NO(2)(+) resulting in intrastrand dimer formation. Insertion of AA opposite the dimerized GG would account for the tandem GG-->TT transversions. Nose-only exposure of Big Blue((R)) mice to PAN at 78ppm (near the MTD) was mutagenic at the lacI gene in the lung (mutant frequency +/-S.E. of 6.16+/-0.58/10(5) for controls versus 8.24+/-0.30/10(5) for PAN, P=0.016). No tandem-base mutations were detected among the 40 lacI mutants sequenced. Dosimetry with 3H-PAN showed that 24h after exposure, 3.9% of the radiolabel was in the nasal tissue, and only 0.3% was in the lung. However, based on the molecular modeling considerations, the labeled portion of the molecule would not have been expected to have been bound covalently to DNA. Our results indicate that PAN is weakly mutagenic in the lungs of mice and in Salmonella and that PAN produces a unique signature mutation (a tandem GG-->TT transversion) in Salmonella that is likely due to a GG intrastrand cross-link. Thus, PAN may pose a mutagenic and possible carcinogenic risk to humans, especially at the high concentrations at which it is present in some urban environments.

Fracture of the medial condyle of the humerus in an elderly patient.

Isolated fractures of the medial condyle of the humerus are rare in any age group and have not been previously reported in the elderly. The case of an 82-year-old who sustained such a fracture is reported. The patient was successfully treated by anatomic reduction and rigid internal fixation. Treatment guidelines and relevant literature are reviewed.

Locus of control and cardiac response to reaction time, mental arithmetic, and time-estimation tasks.

In Exp. 1 subjects, classified on the basis of locus of control scores, performed both reaction time and mental arithmetic tasks. In Exp. 2, similarly classified subjects were required to estimate the duration of a signal with feedback following each trial. Between-groups comparisons in Exp. 1 showed no differences on heart rate or performance measures. This does not support an explanation of differential heart rates during cardiac conditioning based upon cognitive styles of "rejecting" or "accepting" stimuli. Similar comparisons in Exp. 2 indicated significant differences for heart rate and proficiency in time estimation. These differences suggest greater task involvement for internally controlled subjects on feedback tasks, with cardiac acceleration a function of that involvement.