FIG. 2.

Characterization of C₁ structural proteins. Shown at left is an electron micrograph of C₁, showing its polyhedral head, base plate, and three tail fibers (magnification, ×100,000). Shown at right is the protein profile of the C₁ phage obtained by SDS-PAGE. N-terminal sequencing of the two most prominent bands revealed that the 44- and 36-kDa bands correspond to ORF16 and -15, respectively. Whereas ORF15 is consistent with head-tail connector base plate proteins from several phage systems, ORF16 does not share homology with any known proteins. Because ORF16 is the most prevalent structural protein in the C₁ proteome, we speculate that it may represent the major capsid protein.