Introduction

We are now at the beginning of the ``genome age'' in biological research. Several dozen genomes have been completed since the first complete bacterial genome was published in 1995 [Fleischmann et al., 1995]. Microbial genome sequencing projects have become common, and major genome centers are ramping up production to tackle the gigabase genomes of human and other multicellular eukaryotes. Our capacity to sequence DNA has far out-paced our ability to characterize individual gene function experimentally. Now, many thousands of predicted genes exist in the public databases for which we have little or no understanding of their biological function. For example, no functional information is known for more than 50 % of the 19,099 predicted protein coding genes in the recently completed Caenorhabditis elegans genome [C. elegans Sequencing Consortium, 1998]. Much of the next era of biological research will involve assigning basic function to each of these anonymous components, and fitting them into the massively complex networks of interactions within the cell.