Promiscuity of known CM domains in 5 model organisms.

Promiscuity was estimated using a simulation procedure that allows for domain pair duplication (See the text for details). Ab: abundance, defined as the number of proteins containing the domain in a genome. Ap: actual number of combination partners of a domain. Sp: number of combination partners of a domain obtained in simulations. P: empirical probability of observing at most Ap combination partners during simulation of random combinations. A low P value indicates that a domain's actual combination partners are fewer than the results of most random simulations, and indicates that the domain is selective when combining with other domains. For example, in human, the Ap, Sp and P values for the PHD domain are 43, 71.5 and 0.06, respectively; this means that probability P(Sp≤Ap) = 0.06 and, in other words, Ap is less than 94% of simulated Sp values. Conversely, high P value indicates that a domain is promiscuous when combining with other domains. We considered domains with P≤0.2 as selective (marked as underlined in the table) and domains with P>0.8 as promiscuous (marked as bold in the table). Domains with P value in between 0.2 and 0.8 do not deviate from a random combination model. “NA” indicates that the domain is lacking in the organism.