Figure 3. The nonamer FL9 is the naturally processed peptide presented by Qa-1^b molecules.

(a) Progressively N-terminally extended synthetic peptides from the Fam49b R13 fragment were added to Qa-1^b- L cells and tested for their ability to activate BEko8Z. (b) Synthetic FL9, and its N-terminally extended analogs were fractionated on a C18 RP-HPLC column and eluted using a 10-70% acetonitrile gradient. The presence of antigenic activity was assayed by BEko8Z activation. (c) Qa-1^b-expressing COS-7 cells were transfected with the R13 minigene, or (d) a minigene encoding the FL9 peptide, and peptide extracts were fractionated as above. Arrows indicate the peak fractions for the indicated peptides. (e) COS-7 cells that did not express Qa-1^b were transfected with the R13 minigene, and analyzed as above. One representative of three experiments is shown in all panels.