The Oct-1 transcription factor belongs to a family of highly conserved POU domain proteins that participate in the regulation of housekeeping and tissue-specific gene expression. Several isoforms of Oct-1 were described previously. We have found the new alternative promoter of Oct-1 gene and the corresponding mRNA Oct-1X. This mRNA encodes the alternative Oct-1 isoform, which has a truncated N-terminus compared to Oct-1A or Oct-1L isoforms. We explored the expression pattern of this isoform in human tissues and cell lines and demonstrated that it is ubiquitously expressed, but its expression strongly varies in different tissues. Using cotransfection and double luciferase assay, we have demonstrated that Oct-1X is the activator of house-keeping (histone H2B) and tissue-specific genes (B29) transcription.