Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Required for segmental identity of the second through eighth abdominal segments. Once a pattern of abd-A expression is turned on in a given parasegment, it remains on the more posterior parasegment, so that the complex pattern of expression is built up in the successive parasegments. Appears to repress expression of Ubx whenever they appear in the same cell, but abd-A is repressed by Abd-B only in the eight and ninth abdominal segments. Belongs to the Antp homeobox family.