Structural genomics projects aim to provide an
experimental structure or a good model for every protein
in all completed genomes. Most of the experimental work
for these projects will be directed toward proteins whose
fold cannot be readily recognized by simple sequence comparison
with proteins of known structure. Based on the history
of proteins classified in the SCOP structure database,
we expect that only about a quarter of the early structural
genomics targets will have a new fold. Among the remaining
ones, about half are likely to be evolutionarily related
to proteins of known structure, even though the homology
could not be readily detected by sequence analysis.