Nuclease protection assay. Representative mice of three transgenic lines were tested for production of transgene mRNA by a riboprobe protection assay, as described in Materials and Methods.Lane 1, Size standards; lane 2, Tg1.8 (referred to as TgN5Mes in this paper); lane 3, Tg76.3;lane 4, Tg60.8; lane 5, nontransgenic control; lane 6, Tg1.8. All RNA samples tested were from brain, except for lane 6, which was from liver. Either 10 μg of RNA purified by CsCl centrifugation (lanes 2,5, 6) or 20 μg of RNA purified by STAT-60 (Tel-Test “B,” Friendswood, TX) (lanes 3,4) was used. The predicted size of the riboprobe fragment protected by the Gfa2-TK1 transcript (lines Tg1.8 and Tg76.3) is 149 nucleotides, and that protected by the Gfa2-TK2 transcript (Tg60.8) is 113 nucleotides. Both probes were added to the assay of the nontransgenic control.