Figure 3.

Functional analysis of key residues in the HelC and Ccl1 proteins. (Upper) Growth of strains containing HelC WWD, histidine mutations, or Ccl1 WWD mutations under aerobic and anaerobic conditions. Under anaerobic (photosynthetic) conditions, c-type cytochromes, and thus the biogenesis proteins, are required for growth. Plasmids containing either the helC or the ccl1 genes were conjugated into a strain containing a nonpolar deletion of the helC or ccl1 gene, respectively. All strains grow aerobically due to the existence in R. capsulatus of a cytochrome c-independent electron transport pathway (14). (Lower) The WWD domain and flanking histidinyl residues are shown for all three members of the family. +, Residue(s) can be changed and the protein is still functional. Altering His-1 and His-2 of HelC to glycine generates a nonfunctional protein.