Jeong, et al. write:
-
the likelihood that removal of a protein will prove lethal
correlates with the number of interactions the protein has.
For example, although proteins with five or fewer links
constitute about 93% of the total number of proteins, we
find that only about 21% of them are essential. By contrast,
only some 0.7% of the yeast proteins with known phenotypic
profiles have more than 15 links, but single deletion of 62%
or so of these proves lethal. This implies that highly
connected proteins with a central role in the network's
architecture are three times more likely to be essential
than proteins with only a small number of links to other
proteins.
Jeong, H., Mason, S.P., Barabasi, A.L. & Oltvai, Z.N. Lethality and centrality in protein networks. Nature 411, 41-42. (2001).