ANATOMY OF HIGHLY EXPRESSING CHROMOSOMAL SITES TARGETED BY RETROVIRALVECTORS

The eukaryotic genome contains chromosomal loci with a high transcript ion-promoting potential. For their identification in cultured cells, t ransfer of a reporter gene has to be performed by a technique that gra nts the integration of individual copies. We have applied retroviral v ectors in conjunction with inverse polymerase chain reaction technique s to reconstruct a number of these sites for a further characterizatio n. Remarkably, all examples conform to the same design in that the pro cess of retroviral infection selected a scaffold- or matrix-attached r egion (S/MAR) that was flanked by DNA with high bending potential. The S/MARs are of an unusual type in that they show a high incidence of c ertain dinucleotide repeats and the potential to act as topological si nks. The anatomy of retroviral integration sites reveals principles th at can be exploited for the development of predictable transgenic syst ems on the basis of expression and targeting vectors.