Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. First expressed at the 2-somite stage as a stripe in the region of the hindbrain that will give rise to rhombomeres 2 and 3. By the 10-somite stage, expression has expanded posteriorly to rhombomeres 4 and 5. Belongs to the Antp homeobox family. Proboscipedia subfamily.