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Figure 2 | BMC Evolutionary Biology

Figure 2

From: The metazoan history of the COE transcription factors. Selection of a variant HLH motif by mandatory inclusion of a duplicated exon in vertebrates

Figure 2

Compared structure of the COE proteins and coe genes in representative metazoan phyla. (A) Schematic representation and alignment of mouse EBF/COE1 and Drosophila Col. The regions corresponding to the DNA Binding Domain (DBD) and the IPT domain are shown in red and yellow, respectively. The ancestral Helix-Loop-Helix (HLH) motif is represented by two separate black boxes (helices H1 and H2a) and the H1-H2 linker in green. The duplicated helix (H2d) specific to the vertebrate proteins is indicated by a blue box and the C-terminal transactivation domain is in grey. (B) Evolutionary conservation of the coe splice structure. The positions of introns are indicated relative to the different COE protein domains, using the same color code as in (A). Each exon is numbered using the genomic structure of human ebf1 as a reference. The class (0, 1 or 2) of each intron is indicated by a small dot on the corresponding line below each gene. The HCCC zinc finger in the DBD is red dotted. The short linker of variable length and sequence separating the DBD and IPT domains is yellow dotted. The genomic organisations of the DBD/IPT linker region in all COE proteins and the HLH domain in EBF and Ci-COE are surrounded. (C) Sequence alignment between the HLH motifs of EBF and Ci-COE, using the same colour code than in (A). The similarity region of the H1, H2d and H2a α-helical repeats with the HLH repeat of b-HLH proteins is underlined. The duplicated segment in vertebrate proteins extends a few amino acids beyond the predicted α-helical region. The open arrowheads indicate the positions of ancestral introns, with their number indicated. The blue downwards pointing arrowhead indicates the position of the novel intron of vertebrate ebf genes.

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