Figure 5.

Conserved cysteine and histidine residues in yeast Gpi8p are essential for function. (A) Schematic representation of human and yeast Gpi8ps: hatched, dotted, cross-hatched, closed, and open boxes correspond to segments containing amino-terminal signal sequence, highly conserved, nonconserved, transmembrane (TM), and cytoplasmic regions, respectively. The two proteins were divided into four segments, R1–R4, and chimeric molecules were generated. The values in parentheses are percentage amino acid identity between the corresponding regions. Amino acid numbers and the positions of important histidine and cysteine residues are indicated. (B) Activities of a chimeric Gpi8p consisting of human R1, yeast R2, and human R3 and R4, and its alanine mutants. Chimeric Gpi8p and its mutants were transiently transfected into class K cells, and surface expression of CD59 was measured by flow cytometry. Solid and dotted lines indicate staining with anti-CD59 antibody and that with secondary reagent alone, respectively.