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Dark-grown Douglas-fir (Pseudotsuga menziesii [Mirb.J Franco) seedlings had approximately 30% of the major polypeptide of the light-harvesting chlorophyll a/b binding protein, 30% of cab mRNA, 54% of psbA mRNA, and 14% of total chlorophyll, in comparison with amounts in light-grown seedlings. Seedlings entrained under a 24-hour photoperiod of light and dark showed small diurnal fluctuations in cab and psbA mRNA levels and, when transferred to continuous conditions, no circadian rhythms in mRNA levels were apparent. These results suggest that regulation of cab gene expression in Douglas-fir differs from regulation in angiosperms, because in the latter, both light and circadian factors strongly influence the expression of cab genes.

A 1 kb EcoRI restriction fragment cloned from a band visible in an agarose gel of Pinus lambertiana (sugar pine) genomic DNA is present in both subgenera of Pinus with at least 10(4) copies/genome. A full-length copy of this repeated element recovered from a P. radiata (Monterey pine) genomic DNA library was found to possess all of the sequence features associated with gypsy-like retrotransposons. This report describes the biology and history of the IFG (Institute of Forest Genetics) family of retrotransposons. The characterized IFG7 is 5937 bp long. Immediately interior to its 5' and 3' long terminal repeats are sequences consistent with primer binding sites for reverse transcription of the RNA genome. Presumptive gene products associated with retrotransposition appear to be coded in a single reading frame and are in the same order as the gypsy-like retrotransposons and retroviruses. The 1.0 kb EcoRI fragment of IFG elements codes for the 3' half of IFG's reverse transcriptase and the entire RNase H domain. Southern blot analysis suggests IFG was present in Pinaceae before its division into its modern genera. Sequence analysis of IFG 1.0 kb RI fragments and southern analysis also suggest that IFG continued to evolve in Pinus with restriction fragment length polymorphism (RFLP) subfamilies appearing early in the history of each subgenus often correlating with subdivisions of Pinus. Features shared with other plant retrotransposons are also discussed.

Immunoprecipitation of human small nuclear ribonucleoproteins (snRNPs) containing the small nuclear RNAs Ul, U2, U4, U5, and U6 with two antibodies produced in certain patients suffering from systemic lupus erythematosus was used to identify the polypeptides present on human Ul and U2 snRNPs. Ut and U2 snRNPs contain both common and unique polypeptides; visualization of the differences was possible through the use of non-methionine protein labeling and partial fractionation of snRNP populations. To facilitate comparisons with results from other laboratories, we have designated the snRNP polypeptides by their molecular weights. Four small polypeptides, P8, P9, P10, and P12, of 8,000 to 12,000 daltons, are each present in equal amounts on both Ut and U2 snRNPs. Ul snRNPs also contain a unique 30,000-dalton polypeptide, P30, whereas U2 snRNPs contain a unique 27,000-dalton, methionine-deficient polypeptide, P27. A closely migrating pair of polypeptides, P23 and P22, of 23,000 and 21,500 daltons, respectively, is present on both snRNPs; U2 snRNPs are enriched in the former, and Ut snRNPs are enriched in the latter.Nuclei of higher eucaryotic cells contain a family of related small RNAs which exist in the form of small ribonucleoprotein complexes (snRNPs) (8). Certain patients suffering from systemic lupus erythematosus (SLE) produce antibodies directed against snRNPs (6). SLE anti-RNP antibodies selectively immunoprecipitate Ut snRNPs. SLE anti-Sm antibodies define and immunoprecipitate the entire family of Ul, U2, U4, US, and U6 snRNPs. When [33S]methionine-labeled antigen is used, both antibodies immunoprecipitate the same set of polypeptides from murine cells (6). Individual snRNP populations have not been sufficiently fractionated to assign individual polypeptides to individual snRNPs, although several polypeptides have been implicated as the actual SLE antigens (2, 11, 13).It has been suggested that Ut snRNPs provide an adaptor function for RNA splicing through hybridization of Ut RNA sequences complementary to consensus intron sequences at splice junctions (5, 9). The function of the other U snRNPs is unclear, although U2 RNA also appears to contain sequences complementary to at least several exon sequences proximal to splice junctions (7). Both SLE antibodies inhibit the production of mature mRNA in in vitro nuclei, supporting a role for these complexes in RNA biosynthesis (14). Here we present evidence that all human U small nuclear RNAs (snRNAs) are not complexed with the same polypeptides. Instead, there are both common and unique polypeptides associated with at least the two most abundant U snRNAs, Ul and U2, indicating enough dissimilarity in snRNP structure to suggest related but different functions. Nuclei were prepared and washed as described by Lerner and Steitz (6). Low-salt nuclear extracts were prepared by incubating nuclei for 30 min at 20°C in 0.01 M Tris-hydrochloride (pH 8.1)-0.1 M NaCI-1.0 mM MgCl2. High-salt extracts were prepared by incubating similar nuclei for 20 min at 0°C in 0.01 M Tris...