Characterisation of saporin genes: in vitro expression and ribosome inactivation.

A. Saponaria (soapwort) genomic library was screened with a PCR-derived saporin-specific gene probe. The nucleotide sequences of three saporin genomic clones were determined. One of the clones contained a full-length saporin coding sequence whilst the other two were truncated. A hybrid full-length saporin coding sequence was constructed using the two truncated clones. An SP6 promoter sequence and in-frame initiation codon was added to each of the coding sequences using PCR. In vitro translation of saporin coding sequence transcripts in rabbit reticulocyte lysates resulted in the specific depurination of 28S RNA. This indicated that the saporin sequences encoded functional polypeptides with RNA N-glycosidase activity.