STRUCTURE AND EXPRESSION OF UBIQUITIN GENE TRANSCRIPTS IN PINE

Clones encoding polyubiquitin proteins were isolated from a cDNA library derived from Pinus sabiniana phloem tissue. Two different polyubiquitin clones were sequenced. The amino acid sequences of the clones were compared with angiosperm polyubiquitin sequences and with corresponding sequences reported for animal, fungal, and protist polyubiquitins. A computer-aided analysis showed (i) that pine and angiosperm polyubiquitin amino acid sequences correspond perfectly, (ii) that plant polyubiquitins differ from animal polyubiquitins by three amino acids, and (iii) that fungal and protist polyubiquitins are variable, differing by one to eight amino acids from higher organisms. The expression of ubiquitin was studied in bark, cone, needle, phloem, root, and xylem tissues of pine by Northern blot analysis. In all of these tissues, transcripts of about 1000 base pairs were observed. A minor species of 1200 base pairs was seen in longer exposures of autoradiograms. Ubiquitin transcripts were more abundant (in relationship to total RNA) in phloem, cones, and roots than in bark, needles, or xylem.