Genomic organization and alternatively processed forms of Cek5, a receptor protein-tyrosine kinase of the Eph subfamily.

The genomic organization of Cek5, a receptor tyrosine kinase of the Eph subfamily, was elucidated utilizing a strategy involving PCR amplification of Cek5 genomic DNA. Cek5 is the first Eph-related kinase for which the exon-intron structure of the entire coding region has been determined. The Cek5 gene spans over 35 kb and comprises at least 16 exons. The exon-intron structure of Cek5 can be correlated with the proposed domain structure of the Eph subfamily, with the exception of an Ig motif in the extracellular domain. Intron positions in the Cek5 gene coincide with the locations of the deletions, substitutions, or insertions that have been described in a number of Eph-related kinases. This suggests that alternative processing plays a major role in generating the structural variability observed in the Eph subfamily. Consistent with this hypothesis, analysis of the Cek5 gene indicate that: (i) a variant form of Cek5 containing an insertion in the juxtamembrane region (Cek5 +) arises through the use of alternative 5' splice sites, and (ii) a soluble form of Cek5 comprising only the extracellular domain (Cek5s) may exists, which originates by alternative polyadenylation. RT-PCR analysis and RNase protection assays revealed the expression of both Cek5 + and Cek5s at various stages of chicken development.