Deletion of a 150 bp sequence located ~162 bp upstream of the translation start sequence caused decreased gfp expression in the SMB neurons. Within the 150 bp region, we next found four AT- rich DNA sequences that are fully conserved in the pro- moters of the
flp-12 orthologs in the related Caenorhabditis species. Mutations of two AT-rich DNA sequences resulted in an almost complete loss of gfp expression.