© 2005 Nature Publishing Group

DNA has its PCR, but no comparable method exists for high-sensitivity detection of proteins. Now, a new class of protein-DNA chimeras, dubbed "tadpoles," could fill that void.1 "Call this PCR for proteins and other molecules," says coauthor Roger Brent of the Molecular Sciences Institute in Berkeley, Calif.

Tadpoles are chimeric molecules containing a DNA tail and a protein head. The head has affinity for a specific target molecule. The tail, containing a T7 promoter for run-off transcription and a region for PCR amplification, mediates detection.

In tests for biotin and anthrax toxin, tadpoles detected targets across a concentration range of more than 11 orders of magnitude. As few as 600 biotin molecules could be detected with 95% confidence; this sensitivity is one billion times greater than standard ELISA. Measurement takes as little as three hours.

"It potentially allows even modest-affinity aptamers to have the...

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