Identifying important structural characteristics of arsenic resistance proteins by using designed three-stranded coiled coils.

Arsenic, a contaminant of water supplies worldwide, is one of the most toxic inorganic ions. Despite arsenic's health impact, there is relatively little structural detail known about its interactions with proteins. Bacteria such as Escherichia coli have evolved arsenic resistance using the Ars operon that is regulated by ArsR, a repressor protein that dissociates from DNA when As(III) binds.

Structure and pseudosymmetry of cholesterol at 310 K.

The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form [Hsu & Nordman (1983). Science, 220, 604-606], has been fully refined using augmented X-ray data.