A proline-rich transcriptional activation domain in murine HOXD-4 (HOX-4.2).

The product of the murine Hoxd-4 (Hox-4.2) gene is a transcription factor that acts upon an autoregulatory element in Hoxd-4 upstream sequences (1). Using this activity as an assay in transient transfections of P19 embryonal carcinoma (EC) cells, we performed a mutational analysis to map functional domains in the HOXD-4 protein. The importance of the homeodomain was shown by a single amino acid change in this region that abolished activity. Deletion analysis revealed that many evolutionarily conserved regions outside of the homeodomain were dispensable for activation in our assay. Fusions to the GAL4 DNA-binding domain mapped a transcriptional activation function to the HOXD-4 proline-rich N-terminus. The proline-rich transcription factor AP2 squelched activation by HOXD-4 and by GAL4/HOXD-4 N-terminus fusion proteins. Together, these results suggest that HOXD-4 harbors a transcriptional activation domain of the proline-rich type.