The yeast Schwanniomyces occidentalis has a high‐affinity K+ uptake system with a high concentrative capacity, which is able to deplete the external K+ to < 0.03 microM. We have cloned the gene HAK1 of S.occidentalis which complements defective K+ uptake by trk1 and trk1 trk2 mutants of Saccharomyces cerevisiae. When HAK1 was expressed in a trk1 trk2 S.cerevisiae mutant, transport affinities for K+ and other alkali cations resembled those of S.occidentalis. The predicted amino acid sequence of the HAK1 protein shows significant homology with the hydrophobic region of the Kup transporter of Escherichia coli. In S.occidentalis HAK1 expresses in K(+)‐limiting conditions. Our data indicate that in K(+)‐starved cells the system encoded by HAK1 is the major K+ transporter of S.occidentalis.
A 5.5-fold range in breast cancer incidence rates in 21 countries shows strong correlation with national estimates of per capita intake of dietary fat, but not with other caloric sources (proteins and carbohydrates). It is argued that certain breast cancer and hormone factors may contribute little to the explanation of such international variations in incidence of this neoplasm. It is further argued that experimental studies in animals support a specific role for dietary fat in the promotion of mammary tumors, but the effects of calories alone seem to be largely restricted to tumor initiation. Finally, data from international, migrant-population, and analytic epidemiologic investigations are used to motivate the basic relative risk assumption of study designs thus far proposed for the Women's Health Trial, and some continuing motivations for a dietary intervention (low-fat diet) trial are discussed.
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