Some Common Properties Between a Brain Protein that Is Modified by Posttranslational Arginylation and the Microtubule-Associated STOP Protein

Abstract: Properties so far studied of the 125-kDa ¹⁴C-arginylated protein from rat brain show remarkable similarities with those of the STOP (stable tubule only polypeptide) protein. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis the 125-kDa ¹⁴C-arginylated protein moves to the same position as the STOP protein. The 125-kDa ¹⁴C-arginylated protein was immunoprecipitated by the monoclonal Mab 296 antibody specific for neuronal STOP protein. The 125-kDa ¹⁴C-arginylated protein was retained by a calmodulin column like STOP protein. As occurs with the STOP protein, the 125-kDa ¹⁴C-arginylated protein is found in higher proportion in cold-stable than in cold-labile microtubules. However, the modified protein associates with microtubules in a lower proportion than the STOP protein. We conclude that the STOP protein incorporates arginine by a posttranslational reaction but that only a small fraction of the STOP protein shows acceptor capacity in vitro.