Transcriptional properties of genomic transgene integration sites marked by electroporation or retroviral infection

As a possible consequence of their survival strategy, proviruses are predom inantly found in transcription-promoting genomic sites. For certain applica tions, these findings have led to the preferential use of retroviral vector s for the stable integration of transgenes, This study demonstrates that tr anscription levels of single-copy proviruses, which have been established e ither by infection or by single-copy transfection (electroporation), are ra ther comparable. Therefore, electroporation is suggested as an alternative gene transfer route in cases where the use of infectious retroviral vehicle s is to be avoided due to safety considerations. A difference between clone s derived from these two gene transfer routes concerns the inactivation pat tern which, for electroporated clones, is an exclusive property of the low expressers. This difference may be due to the nature of the illegitimate re combination event which is thought to be less invasive if catalyzed by the retroviral integrase. Substantial differences between infection and Ca phos phate-mediated transfection that have been reported earlier are explained b y the respective transfection parameters.