2 PDZ DOMAIN PROTEINS ENCODED BY THE MURINE PERIAXIN GENE ARE THE RESULT OF ALTERNATIVE INTRON RETENTION AND ARE DIFFERENTIALLY TARGETED INSCHWANN-CELLS

Periaxin was first described as a 147-kDa protein that was suggested t o have a potential role in the initiation of myelin deposition in peri pheral nerves based upon its abundance, cell type specificity, pattern of developmental expression, and localization (Gillespie, C. S., Sher man, D. L., Blair, G. E., and Brophy. P. J. (1994) Neuron 12, 497-508) , Here we show that the murine periaxin gene spans 20.6 kilobases and encodes two mRNAs of 4.6 and 5.2 kilobases that encode two periaxin is oforms, L-periaxin and S-periaxin of 147 and 16 kDa respectively. The larger mRNA is produced by a retained intron mechanism that introduces a stop codon and results in a truncated protein with an intron-encode d C terminus of 21 amino acids. Both proteins possess a PDZ domain at the N terminus; nevertheless, they are targeted differently in Schwann cells, Like other proteins that contain PDZ domains, L-periaxin is lo calized to the plasma membrane of myelinating Schwann cells: in contra st, S-periaxin is expressed diffusely in the cytoplasm, This suggests that proteins that contain this protein-binding module may also partic ipate in protein-protein interactions at sites other than the cell cor tex.