AAV with tMCK promoter driven iCre

This AAV expresses iCre driven by a muscle tMCK promoter.

tMCK is constructed by ligating a triple tandem copies of mouse MCK enhancer ( about200 bps each) to the ~100bp mouse MCK basal promoter.). This promoter shows extremely sensitive tissue-specificity: (1) In differentiated C2C12 myotubes, the tMCK promoter is 30-50 fold stronger than the Enh358MCK promoter and 10-20 fold stronger than the CMV promoter; (2) In muscle tissue, tMCK promoter is 15-20 fold stronger than the Enh358MCK promoter, and 3-5 fold stronger than the CMV promoter; (3) Strong tissue-specificity: in liver tissue, the expression level from tMCK promoter is only about 0.3-0.5% of that of the CMV promoter.

Cre is a recombinase from the P1 bacteriophage. This enzyme carries out site-specific recombination between two DNA recognition sites (LoxP sites) through a topoisomerase I-like mechanism. The Cre recombinase here has been codon-optimized leading to a higher level of Cre protein expression (iCre). The 34base pair (bp) loxP recognition site, ATAACTTCGTATA ATGTATGC TATACGAAGTTAT, consists of two 13 bp palindromic sequence which flank an 8 bp spacer region. The products of Cre-mediated recombination at loxP sites are dependent upon the location and relative orientation of the loxP sites. For example, two separate DNA species both containing loxP sites can undergo fusion as the result of Cre-mediated recombination. DNA sequences found between two loxP sites on the same DNA molecule are said to be floxed. In this case, the products of Cre-mediated recombination depend upon the orientation of the loxP sites: DNA found between two loxP sites oriented in the same direction will be excised as a circular loop of DNA, whereas DNA between two loxP sites that are oriented oppositely will be inverted. Besides LoxP sites, other Lox sites have been designed and tested, such as Lox272 and LoxN etc. These Lox elements have been widely used for genetic studies.