IFN increases class I MHC antigen expression on adenovirus-infected human cells without inducing resistance to natural killer cell killing.

It has been previously shown that unstimulated NK cells cannot preferentially lyse adenovirus serotypes 2 and 5-infected human cells. In this study, the ability of IFN to promote the selective NK cell-mediated lysis of adenovirus-infected human cells was determined. The relationship between target cell susceptibility to NK cell-mediated killing and class I Ag expression was also analyzed through the use of adenovirus serotype 2 and 5 mutants that do not make the adenovirus early region 3 19-kDa class I binding protein. IFN induced the selective lysis of adenovirus serotype 2 and 5-infected human cells by activating NK cells (IFN-alpha) and protecting uninfected, but not adenovirus-infected cells, from NK cell-mediated lysis (IFN-gamma). IFN-gamma increased the expression of class I Ag on the surface of cells infected with the adenovirus early region 3 deletion mutants, dl327 or dl801, to a level equal to or greater than that expressed on uninfected cells. Despite the increased expression of class I Ag, IFN-gamma could not protect these adenovirus-infected cells from NK cell-mediated lysis. Thus, dl327 or dl801 infection prevented IFN-gamma's induction of cytolytic resistance to NK cell-mediated killing but left IFN-gamma's induction of class I Ag intact. Surface class I Ag levels were substantially higher on IFN-gamma-treated, dl327-, and dl801-infected cells in comparison to cells infected with wild type adenovirus serotype 5. Again, higher target cell levels of class I Ag did not correlate with increased resistance to NK cell-mediated lysis because there was equivalent NK cell-mediated killing of IFN-gamma-treated adenovirus serotype 5-, dl327-, or dl801-infected cells. Thus, IFN-gamma only protects uninfected cells from NK cell-mediated killing, irrespective of target class I Ag levels, and thereby concentrates NK lytic activity on just adenovirus-infected cells. These data demonstrate that IFN-gamma's ability to protect target cells from NK cell-mediated cytolysis is unrelated to IFN-gamma's induction of surface class I MHC Ag.     

Comparison of statistics for candidate-gene association studies using cases and parents.

Studies of association between candidate genes and disease can be designed to use cases with disease, and in place of nonrelated controls, their parents. The advantage of this design is the elimination of spurious differences due to ethnic differences between cases and nonrelated controls. However, several statistical methods of analysis have been proposed in the literature, and the choice of analysis is not always clear. We review some of the statistical methods currently developed and present two new statistical methods aimed at specific genetic hypotheses of dominance and recessivity of the candidate gene. These new methods can be more powerful than other current methods, as demonstrated by simulations. The basis of these new statistical methods is a likelihood approach. The advantage of the likelihood framework is that regression models can be developed to assess genotype-environment interactions, as well as the relative contribution that alleles at the candidate-gene locus make to the relative risk (RR) of disease. This latter development allows testing of (1) whether interactions between alleles exist, on the scale of log RR, and (2) whether alleles originating from the mother or father of a case impart different risks, i.e., genomic imprinting.     

Transcriptional control, translation and function of the products of the five open reading frames of the Escherichia coli nir operon

Five open reading frames designated nirB, nirD, nirE, nirC and cysG have been identified from the DNA sequence of the Escherichia coli nir operon. Complementation experiments established that the NirB, NirD and CysG polypeptides are essential and sufficient for NADH-dependent nitrite reductase activity (EC 1.6.6.4). A series of plasmids has been constructed in which each of the open reading frames has been fused in-phase with the beta-galactosidase gene, lacZ. Rates of beta-galactosidase synthesis during growth in different media revealed that nirB, -D, -E and -C are transcribed from the FNR-dependent promoter, p-nirB, located just upstream of the nirB gene: expression is co-ordinately repressed by oxygen and induced during anaerobic growth. Although the nirB, -D and -C open reading frames are translated into protein, no translation of nirE mRNA was detected. The cysG gene product is expressed from both p-nirB and a second, FNR-independent promoter, p-cysG, located within the nirC gene. No NADH-dependent nitrite reductase activity was detected in extracts from bacteria lacking either NirB or NirD, but a mixture of the two was as active as an extract from wild-type bacteria. Reconstitution of enzyme activity in vitro required stoichiometric quantities of NirB and NirD and was rapid and independent of the temperature during mixing. NirD remained associated with NirB during the initial stages of purification of the active enzyme, suggesting that NirD is a second structural subunit of the enzyme.     

Analysis of three-dimensional ciliary beating by means of high-speed stereomicroscopy.

Results are presented on the analysis of three-dimensional motion of compound cilia or cirri in voltage-clamped specimens of the protozoan Stylonychia mytilus. Time series of three-dimensional data were obtained by using the anaxial illumination method for simultaneous recording of stereoscopic video images. Data processing involved the following steps: determination of a reference coordinate system based solely on features present in each stereo-pair; tracing of cirral axes in digitized images, conversion to parameter curves by means of least-squares polynomial approximation, conversion of pairs of two-dimensional data to a series of three-dimensional data; correction for distortion due to projective shortening and conversion to a series of polynomial triplets, and analysis of the periodical components of the motion pattern in the frequency domain. Reconstructed beating cycles show typical differences between hyperpolarization-induced ciliary activity and depolarization-induced ciliary activity. Reconstructions of the motion of the basal segment of a cirrus are in agreement with existing data. Analysis of the curvature and torsion of a cirral axis during beating does not reveal any simple pattern of propagated activity within the axoneme. The return stroke may be subdivided into two phases. First, a curvature peak develops proximally. Secondly, a region with increased torsion arises more distally and spreads out in proximal direction. Both curvature and torsion return to minimal values by the beginning of the power stroke.     

Intra-individual length heterogeneity of Rana esculenta mitochondrial DNA

Mitochondrial DNA extracted from Rana esculenta oocytes appears heterogeneous in size. The length of these molecules varies continuously from 18,700 bp to 19,700 bp. Each animal is heteroplasmic and can be characterized by the range of the variation (400-700 bp) and the extreme sizes of the various molecules it carries. The variable region of the genome has been localized between the coding region and the replication origin area.