Expression of G-kinases I and II in UMR106 and C6 cells. (A) UMR106 cells were transfected with expression vectors encoding either G-kinase II (GKII, lane 1, upper panel) or G-kinase I (GKI, lane 1, lower panel) or left untransfected (lanes 2 to 4). Postnuclear homogenates (H), membranes (M), and cytosol (C) were prepared as described in Materials and Methods, and proteins were resolved by SDS-PAGE; Western blots were developed with antibodies specific for G-kinase II (upper panel) or G-kinase I (lower panel). The faster-migrating bands in the upper panel likely represent degradation products of G-kinase II, as they were decreased when denaturing SDS sample buffer was added immediately after cell lysis, as shown in lane 1. (B) C6 cells were transiently transfected with expression vectors encoding G-kinase I (lane 1) or G-kinase II (lane 6) or left untransfected (C6/Wt, lanes 2 and 3); C6 cells stably transfected with G-kinase II are shown for comparison (C6/GKII.1, lanes 4 and 5). Whole-cell homogenates were analyzed by Western blotting as described above.