Cumulative and compensatory effects of competence and incompetence on depressive symptoms in children

The authors tested 5 hypotheses from a competency-based model of child depression using classification and regression tree analysis. The authors obtained measures of 5 domains of competency (i.e., academic competence, social acceptance, sports competence, physical attractiveness, and behavioral conduct) and depressive symptoms that were derived from parent, teacher, peer, and self-reports on 1,063 3rd- and 6th-grade children. Results suggested that (a) multiple domains of competence related to depressive symptoms, (b) significant others' positive evaluations in multiple domains have a cumulative inverse relation to depressive symptoms, (c) negative evaluations in multiple domains have a cumulative but positive relation to depressive symptoms, (d) positive evaluations in one domain somewhat compensate for negative evaluations in another domain, and (e) negative evaluations in one domain offset positive evaluations in another domain.

COOH-terminal processing of nascent polypeptides by the glycosylphosphatidylinositol transamidase in the presence of hydrazine is governed by the same parameters as glycosylphosphatidylinositol addition

Proteins anchored to the cell membrane via a glycosylphosphatidylinositol (GPI) moiety are found in all eukaryotes. After NH2-terminal peptide cleavage of the nascent protein by the signal peptidase, a second COOH-terminal signal peptide is cleaved with the concomitant addition of the GPI unit. The proposed mechanism of the GPI transfer is a transamidation reaction that involves the formation of an activated carbonyl intermediate (enzyme-substrate complex) with the ethanolamine moiety of the preassembled GPI unit serving as a nucleophile. Other nucleophilic acceptors like hydrazine (HDZ) and hydroxylamine have been shown to be possible alternate substrates for GPI. Since GPI has yet to be purified, the use of readily available nucleophilic substitutes such as HDZ and hydroxylamine is a viable alternative to study COOH-terminal processing by the putative transamidase. As a first step in developing a soluble system to study this process, we have examined the amino acid requirements at the COOH terminus for the transamidation reaction using HDZ as the nucleophilic acceptor instead of GPI. The hydrazide-forming reaction shows identical amino acid requirement profiles to that of GPI anchor addition. Additionally, we have studied other parameters relating to the kinetics of the transamidation reaction in the context of rough microsomal membranes. The findings with HDZ provide further evidence for the transamidase nature of the enzyme and also provide a starting point for development of a soluble assay.

A defect in glycosylphosphatidylinositol (GPI) transamidase activity in mutant K cells is responsible for their inability to display GPI surface proteins

The final step in the pathway that provides for glycosylphosphatidylinositol (GPI) anchoring of cell-surface proteins occurs in the lumen of the endoplasmic reticulum and consists of a transamidation reaction in which fully assembled GPI anchor donors are substituted for specific COOH-terminal signal peptide sequences contained in nascent polypeptides. In previous studies we described a human K562 cell mutant line, designated class K, which assembles all the known intermediates of the GPI pathway but fails to display GPI-anchored proteins on its surface membrane. In the present study, we used mRNA encoding miniPLAP, a truncated form of placental alkaline phosphatase (PLAP), in in vitro assays with rough microsomal membranes (RM) of mutant K cells to further characterize the biosynthetic defect in this line. We found that RM from mutant K cells supported NH2-terminal processing of the nascent translational product, preprominiPLAP, but failed to show any detectable COOH-terminal processing of the resulting prominiPLAP to GPI-anchored miniPLAP. Proteinase K protection assays verified that NH2-terminal processed prominiPLAP was appropriately translocated into the endoplasmic reticulum lumen. The addition of hydrazine or hydroxylamine, which can substitute for GPI donors, to RM from wild-type or mutant cells defective in various intermediate biosynthetic steps in the GPI pathway produced large amounts of the hydrazide or hydroxamate of miniPLAP. In contrast, the addition of these nucleophiles to RM of class K cells yielded neither of these products. These data, taken together, lead us to conclude that mutant K cells are defective in part of the GPI transamidase machinery.

An active carbonyl formed during glycosylphosphatidylinositol addition to a protein is evidence of catalysis by a transamidase

Glycosylphosphatidylinositol (GPI) substitution is now recognized to be a ubiquitous method of anchoring a protein to membranes in eukaryotes. The structure of GPI and its biosynthetic pathways are known and the signals in a nascent protein for GPI addition have been elucidated. The enzyme(s) responsible for GPI addition with release of a COOH-terminal signal peptide has been considered to be a transamidase but has yet to be isolated, and evidence that it is a transamidase is indirect. The experiments reported here show that hydrazine and hydroxylamine, in the presence of rough microsomal membranes, catalyze the conversion of the pro form of the engineered protein miniplacental alkaline phosphatase (prominiPLAP) to mature forms from which the COOH-terminal signal peptide has been cleaved, apparently at the same site but without the addition of GPI. The products, presumable the hydrazide or hydroxamate of miniPLAP, have yet to be characterized definitively. However, our demonstration of enzyme-catalyzed cleavage of the signal peptide in the presence of the small nucleophiles, even in the absence of an energy source, is evidence of an activated carbonyl intermediate which is the hallmark of a transamidase.

Cleavage without anchor addition accompanies the processing of a nascent protein to its glycosylphosphatidylinositol-anchored form

Rough microsomal membranes from most mammalian cells, in the presence of a translation system, process nascent proteins with appropriate COOH-terminal signal peptides to their mature glycosylphosphatidylinositol (GPI)-linked forms. The present study, using preprominiplacental alkaline phosphatase as substrate, shows that as much as 10% of the mature product is cleaved correctly but is not linked to GPI. Some of the factors that influence the relative proportions of GPI linked to free mini-placental alkaline phosphatase are the amounts of GPI in the cells and the amino acid substituent at the omega site of the nascent protein. A mechanism for explaining cleavage both with and without GPI addition is presented, which supports a transamidase type of enzyme as the catalyst.

Covariate imbalance and conditional size: dependence on model-based adjustments

Analysis of covariance (ANCOVA) is frequently recommended to correct for covariate imbalance and to control conditional size of hypothesis tests in randomized designs. Such control, however, depends on the accuracy of the ANCOVA model used to make the adjustments. Examination of residuals together with knowledge of the subject matter are important for obtaining an accurate model. Stratified assignment procedures lessen the dependence of proper control of conditional size on the specific model used in the adjustment procedure.

Development of physical ability tests for police officers: a construct validation approach

A construct validation approach was followed to affirm that 8 physical ability test events were significantly related to two important constructs underlying the job performance of police officers: strength and endurance. A sample of 115 incumbent police officers took 8 physical ability tests and were rated by supervisors on their physical performances in their job. LISREL methods were used to test the model specified, and a reasonable fit was achieved. Portions of the model were tested on an independent sample of 161 applicants; the fit of the model was again acceptable. A nomological network of relationships, in which strength and endurance factors correlated in expected directions with other physiological and demographic variables, was hypothesized and tested. Finally, the data were examined for potential gender differences and bias. Considerable differences were shown between men and women on both test and performance variables, and women would be overpredicted if a common regression line were used for selection purposes.

Newly synthesized dengue-2 virus nonstructural protein NS1 is a soluble protein but becomes partially hydrophobic and membrane-associated after dimerization

In a previous paper (G. Winkler, V. B. Randolph, G. R. Cleaves, T. E. Ryan, and V. Stollar, 1988, Virology 162, 187-196) we showed that the newly synthesized dengue-2 virus nonstructural protein, NS1, exists briefly as a monomer and then undergoes dimerization. We demonstrate here that the dimerization of NS1 is associated with a change in hydrophobicity and sedimentability of this protein. Newly synthesized monomeric NS1 is a hydrophilic and water-soluble protein which cannot be pelleted at 75,000 g. After dimerization, however, NS1 showed increased hydrophobicity in a Triton X-114 phase partitioning system and was completely pelletable at 75,000 g; these findings are consistent with NS1 becoming membrane-associated. In experiments in which infected cells were treated with tunicamycin it was shown that the glycosylation of NS1 was not required for either the dimerization or the membrane association.