Premature polyadenylation contributes to the poor expression of the Bacillus thuringiensis cry3Ca1 gene in transgenic potato plants

The cry genes that code for the insecticidal crystal proteins of Bacillus t huringiensis (B.t.) have been widely used to develop insect-resistant trans genic plants. The cry3Ca1 gene has been reported to code for a crystal prot ein which is particularly potent against the Colorado potato beetle (CPB). To explore the biotechnological potential of cry3Ca1, we introduced this ge ne into transgenic potato plants under the control of the CaMV 35S promoter . In the resulting transformants, the cry3Ca1 gene was very poorly expresse d. In fact, no full-length transcript (2300 nt) could be detected. Instead, only short transcripts of approximately 1100 nt were observed. Analysis of these short transcripts by Northern hybridization, RT-PCR as well as by cl oning and sequencing showed that they resulted from premature polyadenylati on. These processing events occurred at four sites within the cry3Ca1 codin g region (at positions 652, 669, 914 and ssi relative to the translation st art site). The sites at which premature polyadenylation took place were not those that showed the highest degree of identity to the canonical AAUAAA m otif. Together with other recent data, our findings suggest that premature polyadenylation is an important mechanism which can contribute to the poor expression of transgenes in a foreign host.