FUNCTIONAL IDENTIFICATION OF THE MOUSE CIRCADIAN CLOCK GENE BY TRANSGENIC BAC RESCUE

As a complementary approach to positional cloning, we used in vivo com plementation with bacterial artificial chromosome (BAC) clones express ed in transgenic mice to identify the circadian Clock gene. A 140 kb B AC transgene completely rescued both the long period and the loss-of-r hythm phenotypes in Clock mutant mice. Analysis with overlapping BAC t ransgenes demonstrates that a large transcription unit spanning simila r to 100,000 base pairs is the Clock gene and encodes a novel basic-he lix-loop-helix-PAS domain protein. Overexpression of the Clock transge ne can shorten period length beyond the wild-type range, which provide s additional evidence that Clock is an integral component of the circa dian pacemaking system. Taken together, these results provide a proof of principle that ''cloning by rescue'' is an efficient and definitive method in mice.