 It is also known as activin receptor-like kinase 1, or ALK1.This gene encodes a type I cell-surface receptor for the TGF-beta superfamily of ligands.It shares with other type I receptors a high degree of similarity in serine-threonine kinase subdomains, a glycine- and serine-rich region (called the GS domain) preceding the kinase domain, and a short C-terminal tail.