Tissue-specific isoforms of the ubiquitous transcription factor Oct-1.

The ubiquitously expressed transcription factor Oct-1 is a member of the POU protein family. It is involved in the activation of snRNA promoters and some mRNA promoters (e.g., promoters and enhancers of genes for histone H2B and immunoglobulins). In this work we have cloned and sequenced a new Oct-1 isoform, named Oct-1L. Both Oct-1L mRNA and Oct-1R mRNA (cloned earlier) are expressed in lymphocytes, but not in any other cell line tested. This is the first report of tissue-specific Oct-1 gene expression. Both these forms differ from the ubiquitously expressed Oct-1 isoforms in the N-termini. They are probably generated by alternative splicing and/or alternative initiation of transcription. The latter is confirmed by the localization of transcription start points upstream of exons 1L (lymphocyte-specific) and IU (ubiquitously expressed). We assume that tissue-specific expression of Oct-1L and Oct-1R in lymphocytes and their structural differences from the ubiquitously expressed Oct-1 isoforms may be related to B and T cell differentiation and/or expression of the immunoglobulin genes.