Analysis of CLK Homology and Expression. Sequence alignment of CLK 1, 2, 3 and 4 indicating the degree of homology among these factors. Also shown are the % sequence identity (B) and sequence similarity (C) among the four kinases. (D) Cells were transfected with a control plasmid (control) or vectors expressing GFP-CLK1 (mCLK1), GFP-CLK2 (mCLK2), GFP-CLK3 (mCLK3), or GFP-CLK4 (mCLK4). Forty-eight hours post-transfection, cells were harvested and extracts fractionated on SDS-PAGE gels. Resultant blots were probed first with anti-GFP antibody to detect individual CLKs then with anti-tubulin antibody to confirm equal loading of samples.