Each of the four arginine residues in the HM-I killer toxin was replaced by
alanine using site-directed mutagenesis, The polymerase chain reaction (PC
R)-constructed mutant gene was successfully expressed in HM-1 toxin resista
nt Saccharomyces cerevisiae. Among four HM-1 toxin analogues, R82A HM-1 tox
in and R86A HM-1 toxin lost killer activity, while R61A HM-1 toxin and R85A
HM-1 toxin retained activity These results strongly indicate the importanc
e of the arginine residues at positions 82 and 86 which are located in the
C-terminal region of the HM-1 toxin for the action of killer activity.