Manipulating large genomic clones via in vivo recombination in bacteria

Transgenesis is proving to be a powerful technique in studying the molecula r genetics of hypertension. The ability to target specific mutations result ing in either loss of function, by gene deletion, the insertion of reporter sequences, or the subtle change of function by nucleotide replacement, can facilitate the understanding of gene function and its role in the manifest ation of diseases. However an inherent problem associated with transgenic s tudies is the lack of consistent expression observed between independent li nes of animals which have integrated the same transgene, a phenomenon known as 'position effect'. Small transgenes are almost invariably subject to po sition effect due to the absence of essential regulatory elements required to maintain an open chromatin structure. This phenomenon may be overcome if larger transgenes, isolated using vectors such as yeast artificial chromos omes (YACs), bacterial artificial chromosomes (BACs) or P1-based vectors, a re used. Studies using such transgenes have reported levels of expression w hich are consistent between lines and dependent upon the number of copies i ntegrated. The introduction of modifications into these large genomic clones is not pr actical by traditional restriction endonuclease strategies and so is depend ent upon in vivo recombination to maintain structural integrity. Here we de monstrate the modification of a 100 Kb P1 clone spanning the renin locus us ing the BAC targeting strategy described by Yang et al (Nat Biotechnol 1997 ; 15: 859-865).