The protein world has a hierarchical and redundant organization that can be specified in terms of evolutionary units of molecular structure, the protein domains. The Structural Classification of Proteins (SCOP) has unified domains into a comparatively small set of folding architectures, the protein fold families and superfamilies, and these have been further grouped into protein folds. In this study, we reconstruct the evolution of the protein world using information embedded in a structural

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... omic census of fold architectures defined by a phylogenomic analysis of 185 completely sequenced genomes using advanced hidden Markov models and 776 folds described in SCOP release 1.67. Our study confirms the existence of defined evolutionary patterns of architectural diversification and explores how phylogenomic trees generated from folds relate to those reconstructed from fold superfamilies. Evolutionary patterns help us propose a general conceptual model that describes the growth of architectures in the protein world.