Surface biotinylation of wild-type Kell and Kp^a transfectants. 293T cells transfected with pRc/CMV-wt (WT) (lanes 2, 5, and 7), pRc/CMV-Kp^a (Kp^a) (lanes 3, 4, and 8) and mock (MOCK) (lanes 1, 6, and 9) were surface biotinylated and the protein extracts immunoprecipitated using streptavidin beads, separated on SDS-PAGE, and immunoblotted with the polyclonal anti-Kell or with anti- tubulin to control for equal amounts of protein in each lane. Total extract refers to cell extracts lysed in Triton X-100 before immunoprecipitation with the streptavidin beads. Biotinylated fraction is the streptavidin immunoprecipitated fraction and therefore constitutes the cell surface-associated proteins. Nonbiotinylated fraction represents the components in the lysed cell extract that was not immunoprecipitated with the streptavidin beads.