A scanning substitution mutagenesis of the 28 bp sequence minimal promoter of
trx-1 identified a bipartite motif composed of two 6 bp elements (CAACCC and AATTAA), separated by a 3 bp linker, being absolutely required for ASJ expression. Mutation of either of the two individual 6 bp elements resulted in the abolishment of GFP expression in ASJ neurons, while mutation of the 3 bp linker did not disrupt GFP expression.