TI - Conclusion . AB - In summary , our data indicate that PHOSphorylation of specific residues regulates Rex-1 function . Utilizing a combination of affinity purification , liquid chromatography tandem mass spectrometry , and site -directed mutational analysis we identified two PHOSphorylated residues , Ser-97 and Thr-174 that are critical for Rex-1 function . Ongoing research in our lab is focused on comparative studies to better characterize the homology of the carboxy terminus of Rex-1 and Rex-2 . These studies are focused on uncovering Rex cellular binding partners and kinases and their functional relationship in order to better understand how PHOSphorylation regulates Rex-1 function . These studies will enable us to determine the differences between the two related proteins and perhaps gain insight into the distinct pathology following HTLV-1 and HTLV-2 infection .