Fig. 2.

Protein function prediction in genomes and metagenomes. Many proteins can be functionally characterized in both data sets. The degree of functional characterization for four metagenomic data sets is shown on the left and for 124 prokaryotic genomes on the right. The inner pie chart represents the level of functional characterization possible by using the homology-based approach. The middle ring shows the level of functional characterization possible by using neighborhood methods. The outer ring summarizes the combined level of characterization possible. Surprisingly, it implies that most metagenomic ORFs (83% of the data) can be functionally characterized, similar to the level possible in fully sequenced genomes.