Screening for unknown mutations by a bioluminescent protein truncation test with homogeneous detection.

The protein truncation test (PTT) is important in screening for unknown mutations that cause premature termination of mRNA translation. PTT involves amplification of the interrogated sequence, in vitro transcription/translation, separation of the generated polypeptides, and detection. In this article, we report a bioluminescent protein truncation test, in which the detection of the nascent protein is performed directly in the expression mixture, within seconds, without the need for separation and purification. A DNA fragment encoding apoaequorin is fused, in-frame, downstream of the interrogated sequence. The fusion product is subjected to in vitro, coupled transcription and translation in the presence of coelenterazine. A wild-type DNA template allows translation to continue after the 3' end of the interrogated sequence, producing a chimeric protein whose C-terminal domain is the photoprotein aequorin. Aequorin is detected, with a high sensitivity, by its characteristic Ca(2+)-triggered, flash-type bioluminescent reaction. Active photoprotein is not produced when a truncating mutation is present in the interrogated sequence. As a model, the method was applied to the detection of truncating mutations in the APC gene (adenomatous polyposis coli).