(A) Schematic diagram of the serine-rich region and transmembrane domain in CPBF8. Numbers indicate amino acid positions from the amino terminus. The filled or hatched box depicts the serine rich region or the transmembrane domain, respectively. (B) Comparison of the carboxyl-terminal region of CPBF proteins. Boxes indicate the putative transmembrane domain. The serine-rich region is underlined. (C) The amino acid sequences of the wild-type and mutated serine-rich regions (SRR). Note that the entire SRR was deleted in CPBF8ΔSRR-HA. The first or second stretch of three serine residues within SRR were substituted with alanines in CPBF8AAA1-HA and CPBF8AAA2-HA, respectively. (D) Localization of CPBF8ΔSRR-HA to phagosomes. Amoebae were incubated with Cell Tracker Blue-stained CHO cells (blue) for 60 min, fixed, and reacted with anti-HA antibody (green). Bar, 10 µm. (E–F) Isolation and identification of binding proteins of CPBF8-HA, CPBF8ΔSRR-HA, CPBF8AAA1-HA, and CPBF8AAA2-HA. Lysates of CPBF8-HA, CPBF8ΔSRR-HA, CPBF8AAA1-HA, and CPBF8AAA2-HA transformants were mixed with anti-HA-antibody-conjugated agarose, washed, and eluted with HA peptide. Immunoprecipitated samples were separated on SDS-PAGE and silver stained (The upper and lower arrow indicated that β-hexosaminidase α-subunit and lysozymes, respectively. (E), or blotted and reacted with anti-HA, β-hexosaminidase α-subunit and lysozyme2 antibody (F).