Fig. 2: The orion gene encodes for a CX₃C motif-containing protein.

a Complementation map of orion with the tested duplications and deficiencies in the 7B–7D region. Duplications are drawn with a heavy line and deficiencies with a light line. If orion⁺ is present on the chromosome carrying a duplication or deficiency, it is indicated in the status column with a “+”; and if it is not present, it is marked “−.” The red line indicates the location of the 72 kb to which orion is mapped based on the complementation results. b Linear representation of the polypeptide chain of the two Orion isoforms. Green represents the common region of the two Orion proteins, blue is the specific N-terminal region of Orion-A, and red the specific N-terminal region of Orion-B. The signal peptide of Orion-A and Orion-B (SP) are colored in light blue or light red, respectively. The CX₃C chemokine motif as well as the location of the orion¹ mutation present in the common region of Orion-A and Orion-B is indicated. c Amino acid sequence lineups of human, mouse, and chicken fractalkines with the common CX₃C-bearing motif of the Drosophila Orion proteins is shown. The number within parentheses after the species’ names indicates the total length of the protein. The underlined sequences in the fractalkine sequences indicate the junctions at which their signal peptides are cleaved. The numbers at the beginning and end of the sequence indicate the protein regions in the lineup. The CX₃C (CXXXC) and conserved downstream cysteines in the fractalkine species are indicated in blue. Fractalkine intramolecular disulfide bonds between conserved cysteines⁴⁷ are specified with brackets. The CX₃C motif in the Orions and the downstream cysteines are indicated in green. The Orion downstream cysteines are offset by one and two amino acids, respectively, from those in fractalkine relative to the CX3C motif cysteines. The Orions differ from fractalkine by the inclusion of considerable extensions upstream to the CX₃C motif, while the fractalkine CX₃C motifs lie within ten amino acids of the mature signal peptide-cleaved proteins. d Orion-B amino acid sequence where the signal peptide is in bold, the three putative GAG binding sites (GAG1, GAG2, GAG3) are highlighted in yellow, the basic residues involved in GAG binding (R = Arg and K = Lys) are in red, and the CX₃C site is in brown. An asterisk is located at the end of the Orion-B-specific amino acid sequence/beginning of the common region. The glycine (GGC) that is mutated to an aspartic acid (GAC) in orion¹ is indicated by an arrow.