Two isoforms of G protein-coupled receptor kinase 4 identified by molecular cloning.

Using PCR we found that G protein-coupled receptor kinase4 (GRK4) mRNA is expressed only in brain out of several tissues tested. In the brain two amplification products were generated. Sequence analysis revealed that the two fragments differed only by the presence or absence of an in-frame-sequence of 96 bp/32 amino acids, located near the N-terminal of the kinase. This demonstrates the existence of two isoforms of GRK4 which were named GRK4A and GRK4B in the presence or absence of the insert, respectively. This is the first evidence that, within the GRKs gene family, different isoforms do exist.