Figure 4.

Substitution of charged residues in the sorting sequence does not alter the ▵ψ dependence of import. (A) b₂-fusion proteins employed. The net charges (amino acid side chains) of the matrix-targeting sequence and the sorting sequence are shown. For comparison, the net charge of the presequences of Su9-DHFR and yeast F₁β is also shown. (B) pb₂(QIC)-DHFR (samples 1–8), pb₂(QIC-Q)-DHFR (samples 9–16), and pb₂(E43Q, D45N)-DHFR (samples 17–24) were imported into mitochondria in the presence of 0–80 μM CCCP, as described in the legend of Figure 1, D and E. The amount of protein imported in the absence of CCCP was set to 100% (control). Bars indicate the SEs of the means (from four to six independent experiments). For comparison, the curves for the import of pb₂-DHFR and pb₂(▵47–65)-DHFR are included (dashed lines).