The nanos promoter drives expression of 'Target-AID', a base editor that targets cytosine in DNA; it favors the conversion of C to T. The 'Target-AID' sequence (from Addgene plasmid 79620) encodes a fusion protein composed of 1. an engineered Cas9 nickase (contains the D10A mutation), 2. cytidine deaminase 1 from sea lamprey (PmCDA1) and 3. the uracil DNA glycosylase inhibitor (UGI) from a Bacillus subtilis bacteriophage (see PMID:27492474).