The single-copy mouse genePtprrgives rise to different protein tyrosine phosphatase (PTP) isoforms in neuronal cells through the use of distinct promoters, alternative splicing, and multiple translation initiation sites. Here, we examined the array of post-translational modifications imposed on the PTPRR protein isoforms PTPBR7, PTP-SL, PTPPBSc42 and PTPPBSc37, which have distinct N-terminal segments and localize to dif-ferent parts of the cell.