Mechanism of Transgene Integration into a Host Genome by Particle Bombardment

DNA sequences of transgenic loci in the transgenes of tobacco and Arabidopsis were analyzed. Almost all transgenic loci studied contained cis elements characteristic of nuclear matrix attachment regions (MARs). A MAR sequence isolated from one such locus of tobacco cells was cloned into the original transformation vector, and introduced into tobacco cells. The presence of the MAR sequence resulted in a five- to tenfold increase in the transformant yields, and it appeared to stimulate both the expression of the transgene and its integration into the host genome. A search using the BLAST program revealed that the transgenic loci contained junction region sequences that may have originated from different chromosomes of the nuclear genome and from the chloroplast genome.