. . "A DNA fragment corresponding to nucleotides 116-413 of the sequence shown in FIG. 1 was cloned into the bacterial expression vector pex 34 A, such that on induction of the bacterial promoter, a fusion protein was produced which contained a part of the MS2 polymerase polypeptide fused to the amino acids of the cytotoxin polypeptide and including the 23 amino acids previously identified." . .