Tel-Abl has increased in vitro and in vivo tyrosine kinase activity relative to p210 Bcr-Abl.

(A) In vitro kinase assay. The c-Abl, p210 Bcr-Abl, and Tel-Abl wild-type (WT; with Tel amino acids 1-336 fused to Abl), ΔPNT, and K581R (KR) proteins were labeled in vivo with³⁵S–l-methionine, immunoprecipitated, and incubated with γ-³²P–adenosine triphosphate and GST-Crk substrate. The top panel is the ³⁵S label, indicating relative levels of expression of the different Abl proteins; the lower panel is the ³²P label, showing levels of autophosphorylation of Abl proteins and transphosphorylation of the GST-Crk substrate. The Crk kinase activity of the different Abl proteins relative to c-Abl after correction for levels of expression is shown at the top. (B) In vivo kinase activity. NIH 3T3 fibroblasts were transduced with empty MSCVneo virus or MSCV virus containing p210 BCR-ABL or TEL-ABL WT, ΔPNT, or KR, and selected for G418 resistance. Lysates were analyzed by Western blotting with anti-Abl (top panel) and antiphosphotyrosine (bottom panel) antibodies.