Examples for intron sliding. Note that all Drosophila species have an intron in these regions and that position changes may have taken place in two steps as the frame would have been maintained in between. (A) NIP region of the gcm2 gene (FBgn0019809). Intron sequences are shown in lower case. The amino acid sequence consensus of the CDS is given beneath the exon sequences. The second conserved glutamine codon between both intron positions has probably supported the shift in a common ancestor of D. pseudoobscura and D. persimilis. This conserved, potential 3' splice site is highlighted in grey. (B) NIP of the CG8516 gene (FBgn0037757). Intron sequences are shown in lower case. The amino acid sequence consensus of the CDS is given beneath the exon sequences. GYRGYR/NAGNAG sites corresponding to the intron shift are highlighted in grey. (C) Conserved part of the intron sequences 616-1 (D. melanogaster, D. ananassae) and 615-1 (D. pseudoobscura) of the CG8516 NIP. Each intron is larger than 300 nt.