Fig. 4. Surface mutations on the Ykt6p longin domain disrupt the targeting of full-length Ykt6p. The same complete set of mutations (Fig. 2, Table 1) were introduced into N-terminally Myc-tagged yeast full-length Ykt6p. Mutants were expressed in PC12 cells as before. Localization of each mutant was examined by co-staining with anti-rat-Ykt6 or anti-syntaxin-1 antibodies. (Top row) The subcellular localization of Myc-tagged yeast Ykt6p mutant proteins E100K/Y101N, F42E and R50E/R56E. (Second row) The localization of the V8N mutant stained with anti-Myc (polyclonal) and anti-syntaxin 1 (47% overlap) antibodies. (Third and fourth rows) Double labeling of mutant-construct-expressing cells with anti-Myc (E10) and anti-Ykt6 antibodies. These constructs displayed 1.6% and 2.6% overlap with endogenous Ykt6, respectively. In the second case, the bright perinuclear area of the mutant was excluded from the calculation owing to obviously coincidental overlap. Scale bar, 10 µm.