Residues involved in Tim44’s interaction with Pam16 fall on one side of Tim44’s predicted N-terminal α-helix. Residues involved in Tim44’s interaction with Pam16 fall on one side of Tim44’s predicted N-terminal α-helix. (A) Overview of Tim44. (Bottom) Residues altered by point mutations previously shown to suppress PAM16 mutations (D’Silva et al. 2008) are marked with a ♦. Residues altered by point mutations isolated in this study are marked with a ★. α-Helical prediction is shown below the sequence. (Top) Residues 174–180 implicated in regulation of Hsp70 binding (Hsp70 reg). Segment 43–209 is sufficient for Hsp70 binding in vitro (Schiller et al. 2008). Dotted line indicates the presequence that is removed upon entry into the matrix and thus not part of the mature protein. (B) Helical wheel showing Tim44 residues from P50 to G83. Red line demarks the hydrophobic side from the hydrophilic side of the helix. Tim44 residues identified in a suppressor screen of a PAM16 mutation are shown in blue. Tim44 residues that were identified in a TS screen using a PAM17 deletion background are shown in orange. Residues marked in gray were found not to have a synthetic interaction with a PAM17 deletion when altered as indicated. (C) Growth phenotype. Tenfold serial dilutions of pam17-Δ tim44-Δ cells carrying a plasmid expressing the indicated Tim44 variants were plated on rich media and incubated at the indicated temperatures for 3 days. Spaces represent separate plates dropped at the same time. Brenda A. Schilke et al. Genetics 2012;190:1341-1353 Copyright © 2012 by the Genetics Society of America