Isolation and DNA sequence of a gene encoding alpha-trichosanthin, a type I ribosome-inactivating protein.

alpha-Trichosanthin (alpha-TCS) is a ribosome-inactivating protein that has recently been shown to inhibit the replication of human immunodeficiency virus. We have isolated a gene encoding alpha-TCS and have determined its DNA sequence. The data indicate that alpha-TCS is synthesized as a preproprotein consisting of 289 amino acids, the first 23 residues of which comprise a putative secretory signal peptide. The last 19 residues comprise a carboxyl extension that has not been reported to be associated with the mature protein and that may be processed in the endoplasmic reticulum or Golgi apparatus of cells producing alpha-TCS. The mature protein consists of 247 amino acids. The sequence predicted by translation of the DNA sequence agrees with and confirms the primary sequence determined recently on the protein. The molecular clone for alpha-TCS will facilitate directed mutational analyses that may provide information on how this peptide, and other ribosome-inactivating proteins, function. These studies may also lead to the development of therapeutic agents with altered activities and/or improved properties for in vivo use.