Figure 7.

Effects of replacement of a histidine with a tyrosine residue in the C-terminal region of colicin D (A) on its cytotoxicity (B), and nuclease activity in vivo (C) and in vitro (D). (B) One microgram of an extract (S100 fraction) prepared from cells producing each mutant colicin was spotted onto a W3110 layer on an agar plate, followed by incubation overnight at 37°C. (C) Cleavage of the intracellular tRNA^ArgICG with various colicin D mutants, as observed on Northern blot hybridization with the probe for tRNA^ArgICG. Arrows indicate the cleaved 3′ fragment of tRNA^ArgICG. (D) Cleavage of the purified and 5′-³²P-labeled tRNA^ArgICG by the purified wild-type (Left) and H611Y (Right) colicin D.