TI - ABL-1 and ABI-1 Interact In Vitro . AB - In mammals , Abl and Abi-2 interact in vitro in two ways . The SH3 domain of Abl binds to a site in the first 157 amino acids of Abi-2 , likely a proline -rich site . The SH3 domain of Abi-2 binds to a proline -rich region near the center of Abl (amino acids 593-730) [49] . To test whether C.elegans ABL-1 and ABI-1 interact directly , we performed in vitro binding experiments with glutathione-S-transferase fused to the N terminus of ABI-1 and in vitro translated portions of ABL-1 . We made two ABL-1 constructs , an N-terminal fragment (amino acids 112-611) and a C-terminal fragment (amino acids 606-1,224) . ABL-1 ( 112-611 ) bound to ABI-1 , but to a small degree also bound to GST alone . Quantitation of the bands using phosphorimagery revealed 8-fold higher binding in the ABI-1 lane than in the GST lane despite a much smaller amount of ABI-1 than GST loaded on the gel ( note Coomassie Blue-stained gel next to the autoradiograph ) ( Figure 7 ) . ABI-1 did not bind to the control Luciferase ; we also failed to observe ABL-1 ( 606-1,224 ) binding . ABL-1 ( 112-611 ) contains the SH3 , SH2 and tyrosine kinase domains of ABL-1 . ABL-1 ( 606-1,224 ) contains the entire C-terminal half of ABL-1 , including the region homologous to mammalian Abl where the Abi-2 SH3 domain binds . However , the polyproline stretch is within the first 60 amino acids of ABL-1 ( 606-1,224 ) and might not have folded appropriately to bind to the ABI-1 SH3 domain . The direct binding of the N-terminal half of ABL-1 to ABI-1 strengthens the hypothesis that a direct interaction between these proteins exists in vivo and suggests that ABL-1 directly inhibits ABI-1 in its roles in the engulfment of apoptotic cells and DTC migration . We also tested whether ABL-1 binds to the product of the abi-1 ( tm494 ) allele , which contains only the first 350 amino acids of the 470 amino acid protein . We called this protein ABI-1Delta . As described above , we made an N-terminal GST fusion to ABI-1Delta and tested whether it bound to ABL-1 . Like ABI-1 , ABI-1Delta bound to ABL-1 ( 112-611 ) but not to ABL-1 ( 606-1,224 ) or to Luciferase ( Figure 7 ) . This result is consistent with the fact that the region of ABI-1 thought to bind to the N terminus of ABL-1 on the basis of mammalian Abl/Abi interactions is intact in ABI-1Delta [49] . Although the amount of ABL-1 ( 112-611 ) bound by ABI-1Delta was approximately 3-fold less than that bound by ABI-1 , it is difficult to know how much ABI-1Delta was loaded onto the gel , because ABI-1Delta comigrates with a nonspecific band . Alternatively , truncation of ABI-1 might cause changes in folding that decrease its ability to bind SUBstrates , which might reflect decreased binding to ABL-1 in vivo and possibly explain the decreased function of the abi-1 ( tm494 ) allele .