Domain composition of CycK, Cdk12, and Cdk13. A) A schematic representation of the CycK domain structure. Two cyclin boxes are depicted with a yellow and green ellipse, and the proline-rich domain by a violet oval. B) Schematic diagrams of Cdk12 and Cdk13 domain structures. Putative or verified nuclear localization signals (NLS) are depicted by asterisks. Arginine/serine-rich (RS), proline-rich (PRM), alanine-rich (A), and serine-rich (SR) domains are indicated by orange, green, violet, and purple ovals, respectively. A yellow asterisk represents the kinase domain (KD). Numbers below the schemes indicate the amino acid position for a given domain.