A family of wheat embryo U2 snRNAs

The U6 small nuclear RNA gene family of potato

Using the inverse polymerase chain reaction (IPCR), 19 U6snRNA gene promoters were isolated from the potato genome. Analysis of their nucleotide sequences revealed the existence of two subfamilies. Promoters from class 1 harbour the typical sequence elements required for plant snRNA gene transcription whereas those from class 2 do not have a TATA box. Three promoters were fused to a modified U6snRNA-coding sequence to allow their activity to be monitored in tobacco protoplasts. Two of the promoters, one from either class, were found to be active. Comparison of potato U6snRNA gene promoter sequences with those found in other plant species showed various degrees of homology. In addition, the entire nucleotide sequences of seven potato U6snRNA genes and one pseudogene were determined. The overall frequency of nucleotide changes after PCR was found to be 1.15 x 10(-3). The mutations appeared to be clustered in a distinct area and were all A-to-G/T-to-C substitutions.

Plant small nuclear RNAs. Nucleolar U3 snRNA is present in plants: partial characterization

Nuclei, isolated from a number of plant species by either of two independent, newly developed methods, regularly contained a common set of low-molecular-mass RNAs. Partial characterization of these RNAs, based on cell fractionation, polyacrylamide gel electrophoretic and chemical sequencing techniques, as well as comparison with literature data, revealed that, in addition to tRNA, 5S RNA and 5.8S RNA, plant nuclei contain two families of low-molecular-mass RNAs, that are counterparts of vertebrate U1 and U5 RNAs respectively, and three individual low-molecular-mass RNA species. One of these may be related to vertebrate U6 RNA. The two others are true eukaryotic U2 and U3 RNAs, respectively, on the basis of the following lines of evidence obtained from analyses of broad bean nuclear RNAs. The 3'-end portion (121 nucleotides sequenced) of broad bean U2 RNA shows a nearly perfect sequence homology with that of authentic pea U2 RNA. Broad bean U3 RNA is localized in the nucleolus and its 3'-end portion (164 nucleotides sequenced) (a) shows sequence homology with that of both rat U3 RNA (48%) and Dictyostelium D2 RNA (39%), (b) has a secondary structure which fits perfectly that proposed for both rat U3 RNA and Dictyostelium D2 RNA, and (c) contains the specific sequence which, in a model based on the primary structure of rat U3 RNA, is supposed to be involved in the processing of eukaryotic 32S pre-ribosomal RNA. This is the first report on the occurrence in plants of nucleolar U3 RNA.