Transcription factor which binds to the cAMP response element (CRE) (PubMed:20023169). Regulates metabolic and innate immune homeostasis, possibly by controlling appropriate expression of genes involved in peritrophic matrix composition and ensuring the normal digestive and immune function of the gut (PubMed:22851689). Required for the expression of odorant receptors Or43b and Or47b (PubMed:26848073). Interacts with Jra/jun; the interaction enhances the DNA-binding activity of Atf3. Moderate expression in some regions of the larval nervous system, the ring gland and imaginal disks. High expression in larval gut, excretory malpighian tubules, salivary glands, and, to a lesser extent, the fat body where levels are approximately 2.5-fold less than the gut. Expressed in embryo and larva with a sharp decline by the late third instar larval stage. Expression peaks 6 hours after puparium formation, drops and remains low until the second day of pupal development and then grows steadily during adult morphogenesis. Mutants die soon after hatching and during all three larval stages with only 2% reaching the third instar larval stage and these die before metamorphosis (PubMed:20023169). Altered expression levels of a number of genes in third instar larvae and chronic inflammation and starvation responses in the larval gut epithelium with a predominance of extremely large lipid droplets and obesity but not hyperglycemia (PubMed:22851689). Belongs to the bZIP family. ATF subfamily. Truncated C-terminus.