Binding of RNA by the alfalfa mosaic virus movement protein is biphasic.

The movement protein of alfalfa mosaic virus was expressed in Escherichia coli and purified by cation exchange chromatography. The purified protein bound single-stranded RNA cooperatively in a biphasic manner. At protein saturation, RNA/protein complexes (designated 'primary complexes') were detected by a nitrocellulose-retention assay within 1 min of mixing, both at 4 and 22 degrees C. In contrast, an incubation of 30 min at 22 degrees C was necessary to obtain electrophoretically retarded complexes ('stabilized complexes'), containing a large number of protein molecules bound stably to each molecule of RNA. Stabilization did not take place at 4 degrees C. The rate of formation of the primary complexes was strongly dependent on protein concentration, and thus appeared limited by a bimolecular interaction. In contrast, the rate of stabilization was independent of protein concentration, suggesting that this process consisted of a rearrangement of the primary complexes without binding of additional protein molecules. In agreement with this suggestion, the amount of complexed RNA at equilibrium was the same when assayed by nitrocellulose retention and by electrophoretic retardation. The possibility that these peculiar kinetics could be caused by the presence of Tween 20 in the incubation media is discussed.

An N-proximal sequence of the alfalfa mosaic virus movement protein is necessary for association with cell walls in transgenic plants.

We have made transgenic tobacco plants (Nicotiana tabacum, cv. Xanthi nc) expressing the movement protein (P3, 300 amino acids) of alfalfa mosaic virus (A1MV) and two N-terminally deleted proteins lacking respectively 12 and 77 amino acids of the P3 sequence (P3 delta[1-12] and P3 delta[1-77]). The same proteins were expressed in recombinant yeast. By subcellular fractionation, the full-length P3 protein expressed by transgenic plants was found to be associated with cell walls as well as with cytoplasmic particulate material, as was the wild type movement protein expressed by A1MV-infected tobacco plants. P3 delta[1-12] behaved similarly but P3 delta[1-77] was found only in the cytoplasm. It thus appears that a polypeptide domain located between amino acids 13 and 77 of the P3 sequence is necessary for association of the protein with cell walls.

[Elimination kinetics of organochlorine compounds in the 1st week of breast feeding]. / Cinétique d'élimination des composés organochlorés au cours de la première semaine d'allaitement maternel.

The elimination kinetics of organochlorine compounds (DDE, lindane, aldrin, heptachlor epoxide and heptachlor) from day 2 to day 10 of breast feeding was studied in 39 volunteers who had a baby in the Maternity Department in Nancy. If there was any contamination of the mothers' milk with DDT, the levels were below the level of detection. In contrast, contamination with DDE was high (112.6 ng/g fat content) on day 2, although it decreased rapidly, to 38.6 ng/g by day 3. On day 2, contamination with lindane, aldrin, heptachlor epoxide and heptachlor averaged 43.8, 23.5, 25.4 and 7.4 ng/g fat, respectively, and the levels showed a linear decrease on subsequent days in all cases except that of heptachlor, for which no significant negative correlation with time could be demonstrated. A breast-fed infant thus absorbs measurable quantities of pesticides but not in excess of the acceptable daily doses. Levels of contamination of human milk in France are lower than those reported in Canadian and Italian studies but are higher than the levels in formulated milk.

Feeding frequency and nitrogen balance in weight-reducing obese women.

In a prospective trial, ten obese women, each her own reference, ate a 1200 kcal/d slimming diet in six meals a day compared with three meals a day during two 14-d periods. Loss of weight was slightly greater during the six-meal periods when loss of nitrogen was lower and thus loss of lean mass was also lower.