Molecular analysis of dicot and monocot small nuclear RNA populations

Oligonucleotides directed against conserved small nuclear RNA (snRNA) sequences have been used to identify the individual U1, U2, U4, U5, and U6 snRNAs in dicot and monocot nuclei. The plant snRNA populations are significantly more heterogeneous than the mammalian or Saccharomyces cerevisiae snRNA populations. U6 snRNA exists as a single species of similar size in monocot and dicot nuclei. The abundance and molecular weights of the U1, U2, U4, and U5 snRNAs expressed in monocot and dicot nuclei are significantly different. Whereas most dicot nuclei contain one or two predominant forms of U2 snRNA and a small number of U4 snRNAs, monocot nuclei contain multiple forms of U2 snRNA ranging from 208 to 260 nucleotides and multiple forms of U4 snRNA from 159 to 176 nucleotides. Multiple forms of U1 and U5 snRNA exist in both plant groups. All prominent size variants of U1, U2, U4, and U5 snRNA identified in monocot nuclei can be immunoprecipitated with anti-trimethylguanosine antibody. We conclude that the sizes and number of snRNA molecules involved in intron excision differ considerably in dicot and monocot nuclei. In wheat nuclei, we have identified an additional U1-like RNA that is differentially expressed during development.