SynopsisMelting profiles were calculated for restriction fragments of $X174 and fd phage DNAs and compared with experimental profiles. The algorithm of Fixman and Freire was slightly modified so that a stability parameter was assigned not to a base pair hut to each nearestneighbor doublet. Stabilities of the 10 kinds of nearest-neighbor doublets were estimated by fitting the calculated profiles to the observed ones. Agreement of the calculated and observed profiles was much improved by this modification. The most interesting finding was that purine (3'-5') pyrimidine stackings are much more stable than their respective reverses. The order of nearest-neighbor stabilities is in excellent agreement with that of negative stacking energies calculated by Rein and coworkers by a quantum-chemical method.

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Dietary, smoking, and drinking habits, as well as sociopsychological factors and familial history, were investigated in a case-control study on the etiology of esophageal cancer (EC) in two areas of Shanxi (Yangcheng and Linfen), north central China. Data were analyzed from 326 cases and 396 controls. We identified several factors associated with high or low risk; some were common across the areas and others were area-specific. Consumption of millet gruel was associated positively with EC, in a dose-response relationship. An increase in EC risk was seen for consumption of millet soup with noodles, and also with certain sociopsychological factors, in both areas. A large increase in risk was found with consumption of boiled vegetables in Linfen, with a dose-response relationship. EC risk tended to become greater with the increasing intake of moldy foods and of pickled vegetable juice. A positive association between EC risk and family history of EC was observed only in Yangcheng. Soybean consumption was found to be associated with reduced risk. Dental hygiene (brushing teeth) was associated with reduced risk in Linfen. There was a suggestion of increased risk associated with heavy tobacco smoking, but it was not significant in either area. Alcohol consumption had a marginally significant association with risk in the high risk area, but not in Linfen.

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A human genomic clone (λhP‐450mc‐1), highly homologous to the rat cytochrome P‐450c gene, was isolated and analyzed for the complete nucleotide sequence. The gene structure coincides with that of a recently reported human gene isolated from genomic DNA of a human breast carcinoma cell line, MCF‐7 [Jaiswal, A. K., Gonzalez, F. J. & Nebert, D. W. (1985) Nucleic Acids Res. 13, 4503–4520] with notable exceptions in the first intron: a 320‐base‐pair fragment is inserted and a 650‐base‐pair fragment is deleted in the gene examined in the present study. The 320‐base‐pair insert appears to contain a moderately repetitive sequence (approx. 140 copies) in the human genome. The 650‐base‐pair fragment, present in intron 1 of the reported sequence, is dislocated in the λhP‐450mc‐1 to about 104 base pairs upstream from the putative transcription initiation site. The results of Southern blot analysis using human total DNA were compatible with the gene structure of λhP‐450mc‐1. A fusion gene, which was constructed by ligating the 5′ flanking region of the gene to the structural gene for prokaryotic chloramphenicol acetyltransferase (CAT), inducibly expressed the CAT activity in mouse Hepa‐1 cells in response to administered methylcholanthrene, indicating that the isolated human gene is indeed of methylcholanthrene inducibility.