Genomic structure of the Cht3 and cathD genes in the Drosophila melanogaster genome. (A) Chromosome 2 illustrating location of Cht3 and cathD genes (red lines) in reference to constitutive heterochromatin (in blue) . Numbers above each red line refer to Flybase cytogenetic placement. (Chromosome not drawn to scale). (B & C) Green arrows represent Flybase-predicted gene regions with corresponding identification. Yellow blocks depict ESTs concordant to the predicted gene region. Blue boxes are predicted exon regions. Red boxes denote LTR position and internal arrows indicate orientation of retroelement. The black line and numbers represent position along the genomic clone sequence which is identified below the figure. Black arrows indicate direction and location of forward (f) or reverse(r) PCR primers. (B) An Antonia LTR fragment (359nt) is inserted in an intron of Cht3 in 12 geographically distinct Drosophila melanogaster strains. (C) A full-length Burdock retroelement, only present in the sequenced y; cn bw sp strain, overlaps the predicted exon boundaries of the cathD gene by 6nt.