Carmo-Fonseca M, Tollervey D, Pepperkok R, Barabino SM, Merdes A, Brunner C, Zamore PD, Green MR, Hurt E, Lamond AI. Mammalian nuclei contain foci which are highly enriched in components of the pre-mRNA splicing machinery. EMBO J. 1991 Jan; 10(1):195-206.