The ins and outs of the transmembrane 4 superfamily.

The recently discovered transmembrane 4 superfamily comprises a group of cell-surface proteins that are characterized by the presence of four hydrophobic domains, which are presumed to be membrane spanning. At least seven of these molecules are expressed on leukocytes, and it seems likely that they mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility.