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 fac tor that acts upon an autoregulatory element in Hoxd-4 upstream sequen ces (1). Using this activity as an assay in transient transfections of P19 embryonal carcinoma (EC) cells, we performed a mutational analysi s to map functional domains in the HOXD-4 protein. The importance of t he homeodomain was shown by a single amino acid change in this region that abolished activity. Deletion analysis revealed that many evolutio narily conserved regions outside of the homeodomain were dispensable f or activation in our assay. Fusions to the GAL4 DNA-binding domain map ped a transcriptional activation function to the HOXD-4 proline-rich N -terminus. The proline-rich transcription factor AP2 squelched activat ion by HOXD-4 and by GAL4/HOXD-4 N-terminus fusion proteins. Together, these results suggest that HOXD-4 harbors a transcriptional activatio n domain of the proline-rich type.