LIGHT REGULATION OF THE ABUNDANCE OF MESSENGER-RNA ENCODING A NUCLEOLIN-LIKE PROTEIN LOCALIZED IN THE NUCLEOLI OF PEA NUCLEI

A cDNA encoding a nucleolar protein was selected from a pea (Pisum sat ivum) plumule library, cloned, and sequenced. The translated sequence of the cDNA has significant percent identity to Xenopus laevis nucleol in (31%), the alfalfa (Medicago sativa) nucleolin homolog (66%), and t he yeast (Saccharomyces cerevisiae) nucleolin homolog (NSR1) (28%). It also has sequence patterns in its primary structure that are characte ristic of all nucleolins, including an N-terminal acidic motif, RNA re cognition motifs, and a C-terminal Gly- and Arg-rich domain. By immuno blot analysis, the polyclonal antibodies used to select the cDNA bind selectively to a 90-kD protein in purified pea nuclei and nucleoli and to an 88-kD protein in extracts of Escherichia coli expressing the cD NA. In immunolocalization assays of pea plumule cells, the antibodies stained-primarily a region surrounding the fibrillar center of nucleol i, where animal nucleolins are typically found. Southern analysis indi cated that the pea nucleolin-like protein is encoded by a single gene, and northern analysis showed that the labeled cDNA binds to a single band of RNA, approximately the same size as the cDNA. After irradiatio n of etiolated pea seedlings by red light, the mRNA level in plumules decreased during the ist hour and then increased to a peak of six time s the 0-h level at 12 h. Far-red light reversed this effect of red lig ht, and the mRNA accumulation from red/far-red light irradiation was e qual to that found in the dark control. This indicates that phytochrom e may regulate the expression of this gene.