The Pfam provides a comprehensive resource of functional and structural families and domains. Each Pfam entry represents a statistical model with an average sequence identity of 30-40% among the members of the family. Currently, Pfam covers 11,912 families, where 1,165 families include at least a viral protein and a eukaryotic protein representative. Some Pfam families are extremely large. Among families that contain metazoa and viral proteins are 'Helix-loop-helix DNA-binding domain' (,6000 proteins) and 'Sugar transporter' (,12,000 proteins). Contamination of viral proteins in metazoan proteomes (e.g., Capsid, Env, Tat) occurs mainly as a result of viral vector manipulations in cell lines, leading to incorrect assignment as a viral-eukaryotic crosstaxa family. An example is the GFP family (PF01353) that we have manually removed from the analysis. To reduce such sporadic instances, we considered Pfam families having at least two metazoan proteins, resulting in a list of 667 Pfam families.