The phosphatidylinositol kinase (PIK) family members fall into two distinct subgroups.
The first subgroup contains proteins such as the PI 3- and PI 4-kinases
and the second group comprises the PIK-related kinases. The PIK-related
kinases include Atm, DNA-PKCS and FRAP. These proteins have in common a
region of homology at their carboxy termini that is not present in the PI 3-
and PI 4-kinases. All of the members of the PIK-related kinases are also over
270 kDa. The Atm gene is mutated in the autosomal recessive disorder ataxia
telangiectasia (AT) that is characterized by cerebellar degeneration (ataxia) and
the appearance of dilated blood vessels (telangiectases) in the conjunctivae of
the eyes. AT cells are hypersensitive to ionizing radiation, impaired in mediating
the inhibition of DNA synthesis and they display delays in p53 induction.
DNA-PK is a heterotrimeric DNA binding enzyme that is composed of a large
subunit, DNA-PKCS, and two smaller subunits collectively known as Ku.