Spliced oct-1 mRNA isoforms with untranslated exons and a partly deleted region coding for the POU-specific domain

Transcription factor Oct-1 is involved in expression regulation of housekeeping genes, in lymphocyte differentiation, and in the immune response. Tissue-specific Oct-1 mRNA isoforms are known to be expressed in lymphoid cells. Four new mouse isoforms were identified. Of these, two were tissue-specific (oct-1Ralpha and oct-1Rbeta) and contained exon I L. The oct-1Ralpha was shown to contain an additional fragment, which corresponds to an exon located in the Y-region of mouse otf-1. No homolog was found in human OTF-1. The oct-1Rbeta isoform proved to lack an exon coding for a fragment of the POU domain. This deletion results in a loss of the first helix of the domain, and the mutant protein is devoid of affinity for octamer ATGCAAAT. Two other mRNA isoforms, oct-1d and oct-1e, were shown to contain untranslated regions between exons 1U and 2. The regions correspond to exons 1i and 2i located between exons 1U and 1L in the Y-region of the mouse oct-1 gene. Human OTF-1 was not found to contain exon 1i. On evidence of these and published data, it was assumed that a set of Oct-1 isoforms is present in the cell, reflecting the complexity of expression regulation of oct-1 and the multiplicity of its functions.