With the availability of complete DNA sequences for many prokaryotic and eu
karyotic genomes, and soon for the human genome itself, it is important to
develop reliable proteome-wide approaches for a better understanding of pro
tein function(1). As elementary constituents of cellular protein complexes
and pathways, protein-protein interactions are key determinants of protein
function. Here we have built a large-scale protein-protein interaction map
of the human gastric pathogen Helicobacter pylori. We have used a high-thro
ughput strategy of the yeast two-hybrid assay to screen 261 H. pylori prote
ins against a highly complex library of genome-encoded polypeptides(2). Ove
r 1,200 interactions were identified between H. pylori proteins, connecting
46.6% of the proteome. The determination of a reliability score for every
single protein-protein interaction and the identification of the actual int
eracting domains permitted the assignment of unannotated proteins to biolog
ical pathways.