CASP, A NOVEL, HIGHLY CONSERVED ALTERNATIVE-SPLICING PRODUCT OF THE CDP CUT/CUX GENE, LACKS CUT-REPEAT AND HOMEO DNA-BINDING DOMAINS, AND INTERACTS WITH FULL-LENGTH CDP IN-VITRO/

Human CDP/cut and its murine counterpart, cux1/CDP are homeodomain rep ressor proteins in the family of Drosophila Cut. Northern blot analysi s reveals complex alternative splicing including forms too small to en code the full 1505 amino acid protein. We have characterized a CDP/cut alternatively spliced cDNA (GASP) of 3.4 kb. Human GASP, a predicted 678 amino acid polypeptide, shares 400 amino acids with CDP, but has a n alternate N terminal exon of 20 aa, and the C-terminal 258 amino aci ds diverge from CDP/cut entirely. As the unique C-terminus of GASP lac ks the three 'cut-repeats' and homeodomain of CDP/cut, we predict it d oes not bind DNA. Murine GASP, 96% similar to human, shares these feat ures. Database searches identify homologs in chicken (86% identical to human GASP) and yeast (29% identical to human). Murine GASP mRNA is u biquitous in mouse tissues and in tissue-culture cell lines. We genera ted a specific antiserum against the unique C-terminus of GASP, and us ed this reagent to demonstrate that GASP protein is expressed as an ap prox. 80 kDa protein in human and murine cells. Go-translation of in v itro-translated GDP and GASP mRNA, followed by immunoprecipitation wit h specific anti-GASP IgG, shows that GASP polypeptide can form a compl ex with CDP. Studies of the intron/exon structure of the murine cux/CD P/mCASP locus (>>100 kb) reveal that the unique 3' exons of GASP are i nterposed between cut-repeats 2 and 3 of the cux gene. We speculate th at a primordial GASP-like gene captured a cut-repeat-homeobox gene to give rise to the eukaryotic Cut/CDP family of proteins. (C) 1997 Elsev ier Science B.V.