Fig. 5. Alanine scanning mutagenesis of the Tail19-55 reporter. (A) Alignment of the sequence of the Tail19-55 reporter and the ten mutants derived from it. The alanines that have replaced the endogenous amino acids are shown in bold. The YXX motif is indicated and was deliberately not mutated as this sequence was likely to be necessary for the efficient endocytosis of the CD8 reporter. Only the serine at position 19 and the glycine at position 55 were left unmutated. (B) The stability of the Tail19-55 reporter and the 10 different mutants was determined by cycloheximide chase as described before. Mutant 7 was the least stable and was predominately present as the lower molecular mass form.