  Natively unfolded proteins exist as an ensemble of flexible conformations
lacking a well defined tertiary structure along a large portion of their
polypeptide chain. Despite the absence of a stable configuration, they are
involved in important cellular processes. In this work we used from three
indicators of folding status, derived from the analysis of mean packing and
mean contact energy of a protein sequence as well as from VSL2, a disorder
predictor, and we combined them into a consensus score to identify natively
unfolded proteins in several genomes from Archaea, Bacteria and Eukarya. We
found a high correlation among the number of predicted natively unfolded
proteins and the number of proteins in the genomes. More specifically, the
number of natively unfolded proteins scaled with the number of proteins in the
genomes, with exponent 1.81 +- 0.10. This scaling law may be important to
understand the relation between the number of natively unfolded proteins and
their roles in cellular processes.
