Isolation and characterization of small nuclear RNAs from Dictyostelium discoideum.

Low molecular weight RNAs were isolated from nuclei of the cellular slime mold Dictyostelium discoideum AX-3. Analysis of the RNAs by polyacrylamide gel electrophoresis showed that the vegetative cell nuclei contained, besides tRNA (Dd1), 5S RNA (Dd4), and 5.8S RNA (Dd7), at least 7 small RNA species (Dd3, Dd5, Dd6, Dd8, Dd9, Dd10, Dd11) of 4S to 8S as major components and that the 7 small RNAs were localized mainly in the nucleus and had no poyl(A) sequence. These nuclear RNA species were metabolically stable, as shown by a chase experiment. Dd6, Dd8, and Dd9 had similar gel electrophoretic mobilities to those of the small nuclear RNA species U1, U2, and U3, respectively, of rat liver. Analysis of the 5'-terminus of these RNA molecules with tobacco acid phosphodiesterase suggested that Dd6, Dd8, and Dd9 each contain a cap. Sequence analysis of the 3'-end labeled Dd9 RNA showed that the 3'-terminal region sequenced had sequence homology with that of rat Novikoff hepatoma U3 RNA. These results indicate that Dictyostelium nuclei contain a set of small nuclear RNA species which is structurally similar to that in mammalian cells. No qualitative differences were detected between the small nuclear RNA species of vegetative and early differentiating cells.