Genomic and cDNA clones coding for the Artemia franciscana homolog of the TATA box-binding protein (TBP) were isolated. The C-terminal region of the predicted protein displays up to 92% sequence identity with the conserved C-terminal regions of TBPs from other species. The gene is divided in seven exons that expand over a region of 33 kb. The position of the four introns located in the conserved C-terminal region has been compared with those of other species. Two of these introns have been generally conserved during evolution, another is an arthropod specific intron, present in Drosophila melanogaster and A. franciscana, and the other is only conserved between vertebrates and A. franciscana. Primer extension experiments detected several transcription initiation sites. Northern blot analyses showed the presence of four mRNAs of estimated sizes of 6.8, 2.6, 1.6 and 1.1 kb. Except for the low expression of the 6.8 and 2. 6 kb RNAs in encysted embryos, steady-state levels showed little variation during the activation of the encysted embryo and the first steps of embryonic and larval development. The amount of TBP protein expressed in encysted embryos and developing larvae has been analyzed by Western blot. Cryptobiotic embryos contain significant amounts of TBP although the level of expression increased almost twice during the first 20 h of development. The presence of TBP protein in cryptobiotic embryos suggests that TBP does not play, by itself, a critical role in the arrest of transcription characteristic of these resistance forms.