Consists of a HindIII/Bsap1407I genomic Csp fragment (containing 4.5kb of 5' regulatory sequences, exon 1, intron 1, exon 2, intron 2 and the 5' portion of exon 3) fused to a 1.9kb cDNA fragment consisting of the 3' portion of exon 3 and exons 4-7 of the Csp-1 isoform.