Fig. 2. (A) The structure of the prt gene. prt contains four exons (1-4) and three introns. The Hobo element is inserted in the first intron of the prt gene that corresponds to 34569 bp in the DS04940 P1 phage. The hobo insertion is indicated by a triangle. The translation start site is in the first exon, marked by a star. Right-angled arrows show the orientation of the primers prt 1F, prt 4R and White 3R, which were used in RT-PCR reactions. (B) Multiple alignment of the amino acid sequences of PRT, human and mouse Sab-s, and C. elegans K03E6.7. Human and mouse Sab have been reported previously (Matsushita, 1998; Yamadori, 1999). The grey background indicates identical residues, and the black background indicates the minimum region required for binding to BTK in the human Sab sequence.