Figure 6. Cyclin T1 TRM and implications for TAR binding. (A) In addition to zinc coordination by Cys261, the residues from TRM helix HC interact with both Tat and AFF4. (B) Modeling of Tat Lys28 acetylation shows the formation of potential H-bond with the side chain of Asn257. The side chains of TRM arginines and lysine are shown as balls-and-sticks. The arrow indicates the location of Tat residue leading to its TAR-binding ARM.