A heterologous probe encoding phenylalanine ammonia-lyase (PAL) was used to identify PAL clones in cDNA libraries made with RNA from young leaf tissue of two Populus delfoides X P. trichocarpa F1 hybrid clones. Sequence analysis of a 2.4-kb cDNA confirmed its identity as a full-length PAL clone. The predicted amino acid sequence is conserved in comparison with that of PAL genes from several other plants. Southern blot analysis of popular genomic DNA from parenta1 and hybrid individuals, restriction site polymorphism in PAL cDNA clones, and sequence heterogeneity in the 3' ends of several cDNA clones suggested that PAL is encoded by at least two genes that can be distinguished by Hindlll restriction site polymorphisms. Clones containing each type of PAL gene were isolated from a poplar genomic library. Analysis of the segregation of PAL-specific Hindlll restriction fragment-length polymorphisms demonstrated the existence of two independently segregating PAL loci, one of which was mapped to a linkage group of the poplar genetic map. Developmentally regulated PAL expression in poplar was analyzed using RNA blots. Highest expression was observed in young stems, apical buds, and young leaves. Expression was lower in older stems and undetectable in mature leaves. Cellular localization of PAL expression by in situ hybridization showed very high levels of expression in subepidermal cells of leaves early during leaf development. In stems and petioles, expression was associated with subepidermal cells and vascular tissues.The enzyme PAL (EC 4.3.1.5) plays a key role in linking primary metabolism to phenylpropanoid metabolism by catalyzing the deamination of L-Phe to produce trans-cinnamic acid. This reaction is considered a key step in phenylpropanoid metabolism (Jones, 1984;Hahlbrock and Scheel, 1989) because it provides an entry point for the biosynthesis of a large number of natural products derived from the phenylpropane skeleton. Consistent with the diverse roles played by these phenylpropanoid-derived compounds, PAL enzyme levels are under both developmental and environmental control (Hahlbrock and Scheel, 1989). The accumulation of PAL mRNA and the activity of PAL promoters varies during the

No abstract

Murine cytomegalovirus infection in spleen cultures resulted in the production of a soluble factor, VISF (virus-induced suppressive factor), which inhibited concanavalin A mitogenesis in fresh spleen cells. Its production was specific for MCMV, since infection of spleen cultures by Sindbis virus, or bacteriophages PM 2 and T 4, and the phagocytosis of latex beads, all failed to elicit VISF. Maximum appearance of the factor occurred within 24 hours p.i. in spleen cultures, and its source was identified as the population of spleen cells which adhered to a plastic culture dish within two hours at 37 degrees C. Non-adherent cells did not produce the factor. Its production was not inhibited by indomethacin. VISF could be concentrated by ultrafiltration on a YM 2 membrane filter, and it was readily fractionated by chromatography on sephadex G-25. In relation to peptides of known molecular weight it appeared to be smaller than 1,400 daltons. Its ability to suppress concanavalin A mitogenesis was largely removed by digestion with proteinase K. Thus VISF appears to be a relatively small peptide or peptide-containing substance. It was purified further by HPLC.

ABSTRACT

No abstract