Research Article Human and yeast z-crystallins bind AU-rich elements in RNA

z-crystallins constitute a family of proteins with NADPH:quinone reductase activity found ini- tially in mammalian lenses but now known to be present in many other organisms and tissues. Few proteins from this family have been characterized, and their function remains unclear. In the present work, z- crystallins from human and yeast (Zta1p) were ex- pressed, purified and characterized. Both enzymes are able to reduce ortho-quinones in the presence of NADPH but are not active with 2-alkenals. Deletion of the ZTA1 gene makes yeast more sensitive to menadione and hydrogen peroxide, suggesting a role in the oxidative stress response. The human and yeast enzymes specifically bind to adenine-uracil rich ele- ments (ARE) in RNA, indicating that both enzymes are ARE-binding proteins and that this property has been conserved in z-crystallins throughout evolution. This supports a role for z-crystallins as trans-acting factors that could regulate the turnover of certain mRNAs.