Genomic structure of the downstream part of the human FLT3 gene: exon/intron structure conservation among genes encoding receptor tyrosine kinases (RTK) of subclass III.

The FLT3 gene encodes a subclass-III receptor tyrosine kinase (RTKIII). We have determined the structural organization of the downstream part of the human FLT3 gene (also designated dsp-FLT3) that corresponds to the intracellular region of the protein. The coding region is spread over twelve exons spanning 10 kb of genomic DNA. Exon sizes range from 83 to 154 bp, while intron sizes range from 86 bp to more than 1.9 kb. Comparison with the corresponding domain of other RTKIII genes (KIT and FMS) shows that these genes share the same number of exons, which are highly conserved in size, sequence and exon/intron boundary positions. In addition, the intron phase of equivalent introns of FLT3, KIT and FMS are all identical. Our results reinforce our hypothesis based initially only on the KIT and FMS comparison showing that RTKIII genes share a common structural organization and have evolved from a common ancestor gene by cis and trans duplication. Comparison of the genomic organization of the intracellular-encoding part of RTKIII genes with that of RTKI, II and IV genes shows that subclasses III and IV are the most closely related.