Examples of classes of proteins containing the FA region. The figure shows the modular organisation of FA region proteins in schematic outline. The proteins all contain FERM domains in their N-terminal region (although splice variation at certain N-termini can add extra sequence upstream of the FERM domain). On the C-terminal side of the FERM and FA regions are diverse sequences. Examples shown are as follows. (a) The true 4.1 proteins have a C-terminal domain (CTD) that binds receptors; and in mammals a spectrin-actin binding domain (SAB) promotes the binding of spectrin to actin. There are four such in vertebrate genomes, and one such in invertebrate genomes. (b) A group of poorly characterised proteins (two in vertebrate genomes, one in invertebrates) have FERM and FA regions, plus transmembrane segments in their C-terminal regions. They have no N-terminal signal sequences, and appear to be Type II membrane proteins. (c) The non-receptor tyrosine phosphatase protein PTP-MEG1 in mammals, PTP-MEG (split central complex) in fly and protein-tyrosine phosphatase 1 in worm are non-receptor tyrosine phosphatases localised at membranes; they have roles in control of cellular proliferation and control of interaction with extracellular matrix. Notably, the FA region was not found in the other FERM domain phosphatases PTPH1, PTP-E1 and PTP36. (d) CDEP is a GEF for Rho family GTPases. The FA region is also found in the related FARP2 gene product. (e) A variety of other proteins lack further domains recognised by SMART or Pfam. These include Band 4.1-like protein 5 and NBL-4.