DISSECTION OF THE ABILITY OF THE CHICKEN LYSOZYME GENE 5'-MATRIX ATTACHMENT REGION TO STIMULATE TRANSGENE EXPRESSION AND TO DAMPEN POSITIONEFFECTS

The chicken lysozyme gene domain is flanked by nuclear matrix attachme nt regions (MARs) on each side. We have previously shown that bilatera lly flanking 5' MARs in stably transfected artificial genetic units en hance expression of a reporter transgene and dampen position effects o f the chromatin structure at the site of integration. The 5' MAR was n ow dissected into smaller fragments that were monitored for effects on transgene expression in mouse 3T3 cells by a similar assay. Fragments , which contain 1.32 and 1.45 kb and represent the upstream and the do wnstream half, respectively, of the 5' MAR, retained the ability to st imulate transgene expression as well as the ability to reduce the vari ation in the level of expression. However, a 452 bp subfragment (H1-Ha eII), which still exhibits specific binding to nuclear matrices and co ntains two high-affinity binding sites for the abundant nuclear matrix protein ARBP, lost both of those abilities. A dimerized 177 bp sequen ce from fragment H1-HaeII, which also binds selectively to nuclear mat rices and includes a duplicated ARBP binding site, was also unable To stimulate reporter gene expression. Furthermore, a 0.65 kb subfragment containing an intrinsically bent sequence did not affect an elevated reporter gene expression and its dampening. Our results show that the ability of MAR fragments to bind to nuclear matrices is not sufficient to enhance and insulate transgene expression in stably transfected ce lls.