Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Plays an important role in the patterning of hindbrain and pharyngeal arches. First expressed at the 1-somite stage in the presumptive rhombomeres 3 (r3) and 5 of the developing hindbrain. By the 3- to 4-somite stages, r5 expression has increased and there is weak expression in r4 and posterior to r6. From the 10- to 20-somite stages, confined to r3, r4 and r5 with highest levels in r3 and lowest levels in r5. Belongs to the Antp homeobox family. Proboscipedia subfamily.