To identify Plk4-specific phosphorylation sites, we subjected in vitro phosphorylated GCP6 to mass spectrometry and identified ten Plk4-specific phosphorylation sites on serine residues.
The majority of the Plk4 phosphorylation sites were found within the tandem repeat segment of GCP6 (nine tandem repeats of a 27 amino acid sequence are present in GCP6).