As Actinobacteria lost the OM without lengthening SRP RNA (Rosenblad et al. 2009), this is not the only possible response to OM loss, but its happening in two independent groups means that SRP expansion by a new arrest domain was almost certainly an adaptive response to OM loss in both Clostridia/Bacilliia and stem neomura. Here, UCN2 is linked to ocular melanoma.