Fill in the Blank in the Following Paragraph Regarding the Recognition

Short Answer

Fill in the blank in the following paragraph regarding the recognition of tail-anchored proteins by their targeting machinery. DO NOT use abbreviations.
"When the hydrophobic transmembrane ? helix at the C-terminus of an ER tail-anchored protein emerges from the ribosome, the tail-anchored-binding domain (TABD) of the Get3 ATPase binds to it. The job of TABD in Get3 is similar to that of the flexible hydrophobic domain in the SRP54 protein of the signal-recognition particle, in that it also has to recognize a degenerate set of hydrophobic ?- helices. Therefore, it is not surprising that, just like the corresponding domain in SRP54, the binding site in Get3 is rich in ... residues."