The invention relates to a novel ribosome-binding protein derived from
Bougainvillea spectabilis having a molecular weight of about 26,000
daltons by polyacrylamide gel electrophoresis under reducing and
non-reducing conditions, a pI of about 9.0, and a specified
amino-terminal amino acid sequence. The invention further relates to a
conjugate of the protein with a targeting ligand, such as an antibody, to
form an immunotoxin. The protein and the conjugate are useful in therapy,
for example, in the control of tumour cells or viruses.