FIG. 5.

SL1 of U1 snRNA inhibits the assembly of Sm core in vitro. HeLa extracts were added (+) to nonradioactive SL1 or SL1A3 and incubated for 30 min on ice. Subsequently, [³²P]UTP-labeled U1, U2, U4, or U5 snRNA was added to the preincubated extracts and the mixtures were further incubated for 30 min at 30°C; as a control, the extracts were also mixed with [³²P]UTP-labeled U1, U2, U4, or U5 snRNA, respectively, in the absence of nonradioactive RNAs (lanes 2, 6, 10, and 14). The formation of Sm cores was analyzed by electrophoresis on native 6% polyacrylamide gels and autoradiography.