Analysis of gene function in vivo is typically done one gene at a time, by expressing a DNA construct in cells that over- or under-produce the gene, and then analyzing the effects on cellular physiology. Using protein microarrays for this purpose would be attractive, but they are more technically challenging to create and use than nucleic acid arrays because different proteins require different conditions to maintain their properly folded forms. Taking a different tack, researchers at the Whitehead Institute reported in last week's Nature that they have developed microarrays of transfected mammalian cells that express a variety of proteins.

The cell microarrays are prepared