Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Binds the consensus region 5'-TTAAT[GT][GA]-3'. This homeotic protein controls development of the cells in the posterior thoracic and first abdominal segments. In the embryo (at 20% embryogenesis), expression is highest in the first abdominal segment (A1) with significant but diminishing levels in more posterior thoracic segments (T1 and T3). The QA motif is able to mediate transcriptional repression. Belongs to the Antp homeobox family.