Expression of Replication-Independent Chicken H3.3 Histone Gene without Introns

We eliminated introns from replication independent chicken H3.3 histone gene using a H3.3 cDNA clone and a genomic H3.3 clone. After introduction into Rat 3 cells, we observed its pattern of expression by analyzing mRNA from different phases of the cell cycle. Even without introns, the H3.3 gene was expressed constitutively at a low level throughout the cell cycle. This indicates that the introns in the H3.3 gene are not responsible for the cell cycle-independent expression of the gene. This result contradicts previous reports that suggested their importance in cell cycle regulated expression. We believe that other regions of the gene, promoter, coding region, and/or 3'-end of the gene, are involved in its expression pattern.