Molecular basis for a polymorphism involving Fc receptor II on human monocytes

IgG Fc receptor II (Fc gamma RII) on human monocytes is polymorphic with respect to its appearance on gels after isoelectric focusing and with respect to its ability to mediate T lymphocyte proliferation induced by murine anti-CD3 mAb of the IgG1 isotype (i.e., its ability to bind murine IgG1). To determine the molecular basis for this polymorphism, we isolated total cellular RNA from PBMC of responders and nonresponders (defined by Leu-4-induced [3H] thymidine incorporation) and synthesized corresponding cDNA. Sequences encoding the extracellular domain of Fc gamma RII were then amplified using the Taq polymerase chain reaction. Amplified DNA fragments were cloned into pUC vectors, and sequenced. Analysis of clones from two nonresponders revealed a single base change (G for A) at position 519, which would result in the substitution of a histidine for an arginine at residue 133 in the mature Fc gamma RII protein. These findings suggest that the polymorphism involving human monocyte Fc gamma RII results from allelic variation of a single gene.     

Analysis of the most representative tumour-derived p53 mutants reveals that changes in protein conformation are not correlated with loss of transactivation or inhibition of cell proliferation.

In an effort to correlate the biological activity of the p53 protein with its conformation, we analysed 14 p53 mutants representative of the most frequently observed protein alterations in human cancers, at codons 175, 248 and 273 (22% of all mutations thus far reported), all three of which contained a CpG dinucleotide. Strikingly, most of the mutants at codons 248 and 273 did not display any change in their conformation, as probed by monoclonal antibodies PAb240 and PAb1620 or by binding to hsp70 protein. For all 14 mutants tested, we found a strict correlation between the transactivation properties of p53, tested either on RGC sequences or using the WAF-1 promoter, and inhibition of cell proliferation. All these mutants showed nuclear localization. Several mutants, present at a low incidence in human tumours, displayed wild-type activity in all our assays, suggesting that the presence of a mutation is not strictly correlated with p53 protein inactivation in tumours. Further analysis of nine thus far undescribed p53 mutants at codon 175 revealed a wild-type or mutant behaviour. All these results suggest that the occurrence of a mutation is dependent on two criteria: (i) the mutability of a given codon, such as those containing a CpG dinucleotide; (ii) the resulting amino acids, eventually leading to synthesis of a p53 conferring a growth advantage on the cell.     

Decreased lipolysis in peanuts by a pyridazinone bioregulator

Peanut,Arachis hypogaea, plants were treated in the field with the bioregulator BAS 105 00W, 4-chloro-5-dimethylamino-2-phenylpyridazin-3-one, a substituted pyridazinone, at different times of development. The seeds were harvested, dried, hand-shelled, and analyzed for lipoxygenase activity and conjugated diene hydroperoxide content. Reduced lipoxygenase activity occurred when the bioregulator was applied to the plants at flowering and pegging. The conjugated diene hydroperoxide content decreased the most in peanuts when the bioregulator was applied at pegging. The apparent K_m for lipoxygenase of treated peanuts with linoleic acid as substrate was the same as that for untreated peanuts.