In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins is spatially and temporally regulated during embryonic development. HOXA9 is part of the A cluster on chromosome 7 and encodes a DNA-binding transcription factor which may regulate gene expression, morphogenesis, and differentiation. HOXA9 is highly similar to the abdominal-B (Abd-B) gene of Drosophila. A specific translocation event which causes a fusion between HOXA9 and the NUP98 gene has been associated with myeloid leukemogenesis. Read-through transcription exists between this gene and the upstream homeobox A10 (HOXA10) gene.