Segment polarity protein that provides positional cues for the development of head and thoracic segments. Regulates the expression of zygotic genes, possibly through its homeodomain, and inhibits the activity of other maternal gene products. May also bind RNA. Interacts with Bin1 to repress transcription of bicoid target genes in the anterior tip of the embryo; a process known as retraction. Interacts with Bin1; in vitro and yeast cells. Interacts with bin3. Maternal expression is an anterior cap concentrated in the cortical cytoplasm. Expressed both maternally and zygotically. Belongs to the paired homeobox family. Bicoid subfamily.