Figure 7

Evolutionary model for type VI IF proteins. Fugu lacks obvious nestin homologs [38] and NF proteins may well represent ancestral type VI IF proteins [8]. Our model proposes that the first type VI IF protein resulted from the fusion of a RPGR-like cassette C-terminal to a NF gene. The C-terminal domain of a tanabin-like protein may have evolved giving rise to the HR domain displaying nucleotide hydrolysis activity in birds whereas this activity was progressively lost in mammalian nestins. In addition, the HR domain may have been duplicated and conserved in a mammalian gene that is not part of the IF family.