Schematic diagram of the pSRαMSVtkneo–NPM-ALK retroviral vector carrying the NPM-ALK fusion gene cloned into the HindIII (H) restriction endonuclease site of pSRαMSVtkneo. The NPM-ALK gene is translated from viral Moloney sarcoma virus long terminal repeat (LTR)-directed transcripts. The coding sequence for the bacterial neo gene (neomycin phosphotransferase) is transcribed from an internal herpes simplex virus thymidine kinase (tk) promoter region. Indicated on the diagram is the unique EcoRI (E) restriction endonuclease recognition site in pSRαMSVtkneo, which permits assessment of proviral integration sites; the location within NPM-ALK of the murine Alk cDNA probe used in Southern analyses of proviral integration, a 187-bp fragment that encodes the juxtamembrane segment of the receptor protein, is represented by a solid black bar. The 2; 5 translocation fuses the amino-terminal portion of NPM to the entire intracellular region of ALK, which includes the tyrosine kinase domain. MB, putative metal binding domain of NPM. The segment of ALK (amino acids 419 to 520, inclusive) recognized by the polyclonal antibody anti-ALK 11 is also shown.