A genomic fragment of cid is expressed from its own promoter and has EGFP fused within the fragment 11 amino acids before the start of the histone fold.

P{gcid-EGFP-cid} is composed of three distinct fragments. First, a 772 bp cid PCR fragment encompassing 412 bp upstream of the cid translational initiation codon and 354 bp of the coding region up to codon 118. Second, a PCR fragment encompassing the cid region coding for amino acids 119 through 225 as well as 513 bp of the flanking 3' genomic region. A third fragment encompassing the EGFP coding region, and flanked by three glycine residues at both sides to serve as flexible linkers, is inserted between the cid codons specifying amino acids 118 and 119. Thus, EGFP is inserted within the N-terminal tail of the cid protein.