| Summary: | The structure of the mouse periaxin gene (prx) has been determined. This was in order to facilitate further studies on the molecular genetics of periaxin expression and function. Analysis of the structure and expression of the mouse periaxin gene has revealed that the gene encodes two polypeptides and the mechanism by which these two proteins are encoded has been established. Furthermore, the localization of these two proteins has been shown to differ in myelinating Schwann cells. A mouse genomic library constructed in the bacteriophage replacement vector Lambda Dash II was screened by plaque in situ hybridization using a full length rat periaxin cDNA as probe. Clones covering the entire length of the gene were isolated and fully characterized. The murine periaxin gene spans 20.6 kb, includes seven exons and encodes two mRNAs of 4.6 and 5.2 kb. The largest of these exons is 4 kb in length and encodes 90% of the protein coding sequence and all of the 3' untranslated region. Sequence analysis of the gene's core promoter identified several interesting features. A TATA-box motif is absent; hence the murine periaxin gene promoter belongs to the TATA-less family. Direct comparison with the promoters of myelin genes expressed in Schwann cells detected several common motifs, the most important of which is known to bind the transcription factor SCIP/Oct-6. This factor has been shown to have a vital role in the regulation of myelination by Schwann cells. Such features underline the potential importance of periaxin in the myelination process. The 4.6 kb mRNA includes all seven exons and encodes the previously described protein of 147 kDa (now termed L-periaxin). The 5.2 kb mRNA, in addition to the seven exons, also includes an intron comprising 600 bases located between exon 6 and 7. The differential localization of L-periaxin and S-periaxin indicates that they serve distinct functions in the myelinating Schwann cell.
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