APOLIPOPROTEIN-B GENE-EXPRESSION IN A SERIES OF HUMAN APOLIPOPROTEIN-B TRANSGENIC MICE GENERATED WITH RECA-ASSISTED RESTRICTION-ENDONUCLEASE CLEAVAGE-MODIFIED BACTERIAL ARTIFICIAL CHROMOSOMES - AN INTESTINE-SPECIFIC ENHANCER ELEMENT IS LOCATED BETWEEN 54 AND 62 KILOBASES 5' TO THE STRUCTURAL GENE

Prior studies have established that the expression of the human apolip oprotein B (apoB) gene in the intestine is dependent on DNA sequences located a great distance from the structural gene. To identify the loc ation of those sequences, we used recA-assisted restriction endonuclea se (RARE) cleavage to truncate the 5'- or 3'-flanking sequences from a 145-kilobase (kb) bacterial artificial chromosome spanning the entire human apoB gene. Seven RARE cleavage- modified bacterial artificial c hromosomes with different lengths of flanking sequences were used to g enerate transgenic mice. An analysis of those mice revealed that as li ttle as 1.5 kb of 3' sequences or 5 kb of 5' sequences were sufficient to confer apoB expression in the liver. in contrast, apoB gene expres sion in the intestine required DNA sequences 54-62 kb 5' to the struct ural gene. Those sequences retained their ability to direct apoB expre ssion hn the intestine when they were moved closer to the gene. These studies demonstrate that the intestinal expression of the apoB gene is dependent on DNA sequences located an extraordinary distance from the structural gene and that the RARE cleavage/transgenic expression stra tegy is a powerful approach for analyzing distant gene-regulatory sequ ences.