Tagging of a maize gene involved in kernel development by an activated Uq transposable element

Summary A quiescent Uq transposable element has been activated in a maize plant treated with 5-aza-2-deoxycyti-dine. This activated Uq cosegregates with a heritable dominant miniature (Mn) kernel phenotype, indicating its physical association with a maize miniature locus (Mn:: Uq). The Mn:: Uq mutant is dominant in producing a miniature seed phenotype of variable size and in reducing seedling vigor in the early growth stage. Genetic experiments indicate that the Mn:: Uq mutant also affects the activity of the male gametophyte, whereby pollen germination is inhibited, thus lacking pollen tube growth resulting in the male nontransmissibility of this mutant. Proof for the Uq element in this mutant is derived by its ability to transactivate the standard a-ruq reporter allele to yield spotted aleurone tissue. However, the Mn:: Uq mutant does not transactivate a normally Uq-responsive c-ruq allele, suggesting a structural difference between the two ruq receptors at the A1 and C1 loci. It is anticipated that cloning of the Uq transposable element would facilitate the molecular cloning and characterization of the maize miniature gene.Journal Paper No. J-13425 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, USA, Project No. 2850     

Partitioning of Noncyclic Photosynthetic Electron Transport to O(2)-Dependent Dissipative Processes as Probed by Fluorescence and CO(2) Exchange

The partitioning of noncyclic photosynthetic electron transport between net fixation of CO₂ and collective O₂-dependent, dissipative processes such as photorespiration has been examined in intact leaf tissue from Nicotiana tabacum. The method involves simultaneous application of CO₂ exchange and pulse modulated fluorescence measurements. As either irradiance or CO₂ concentration is varied at 1% O₂ (i.e. absence of significant O₂-dependent electron flow), the quantum efficiency of PSII electron transport (_se) with CO₂ as the terminal acceptor is a linear function of the ratio of photochemical:nonphotochemical fluorescence quenching coefficients (i.e. q_Q:q_NP). When the ambient O₂ concentration is raised to 20.5% or 42% the q_Q:q_NP is assumed to predict the quantum efficiency of total noncyclic electron transport (′_se). A factor which represents the proportion of electron flow diverted to the aforementioned dissipative processes is calculated as (′_se − _se)/′_se where _se is now the observed quantum efficiency of electron transport in support of net fixation of CO₂. Examination of changes in electron allocation with CO₂ and O₂ concentration and irradiance at 25°C provides a test of the applicability of the Rubisco model to photosynthesis in vivo.     

Expression of the Major Light-Harvesting Chlorophyll a/b-Protein and Its Import into Thylakoids of Mesophyll and Bundle Sheath Chloroplasts of Maize

Distribution of the major light-harvesting chlorophyll a/b-protein (LHCII) and its mRNA within bundle sheath and mesophyll cells of maize (Zea mays L.) was studied using in situ immunolocalization and hybridization, respectively. In situ hybridization with specific LHCII RNA probes from maize and Lemna gibba definitively shows the presence of high levels of mRNA for LHCII in both bundle sheath cells and mesophyll cells. In situ immuno-localization studies, using an LHCII monoclonal antibody, demonstrate the presence of LHCII polypeptides in chloroplasts of both cell types. The polypeptide composition of LHCII and the amount of LHCII in bundle sheath cells are different from those in mesophyll cells. Both mesophyll and bundle sheath chloroplasts can take up, import and process the in vitro transcribed and translated LHCII precursor protein from L. gibba. Although bundle sheath chloroplasts incorporate LHCII into the pigmented light-harvesting complex, the efficiency is lower than that in mesophyll chloroplasts.     

Transgenic HLA-DR alpha faithfully reconstitutes IE-controlled immune functions and induces cross-tolerance to E alpha in E alpha 0 mutant mice

We have constructed transgenic mice that express the human class II MHC molecule HLA-DR alpha on a genetic background in which the equivalent endogenous gene, H-2 IE alpha, is not expressed. In these mice, DR alpha complemented the E beta chain such that tissue-specific expression of an interspecies hybrid DR alpha-E beta heterodimer was obtained. Despite 25% amino acid differences between DR alpha and E alpha, immune responsiveness to IE-controlled antigens, clonal deletion of IE-reactive T cells, and alloantigenicity were quantitatively and qualitatively indistinguishable in IE-positive mice and in mice that had integrated at least four copies of the transgene. These results demonstrate a remarkable degree of structural, regulatory, and functional conservation. They also suggest that tolerance induction involves only discrete portions of MHC molecules.     

Proteins binding to site C2 (muE3) in the immunoglobulin heavy-chain enhancer exist in multiple oligomeric forms.

We describe the purification to near homogeneity of proteins binding to site C2 (muE3) in the immunoglobulin heavy-chain enhancer. Proteins binding to this site produce four protein-DNA complexes which are distinguished by their mobility in gel retardation assays and their elution properties in an anion exchange column. DNA affinity-purified preparations of three chromatographically separated pools, containing different subsets of the four complexes, each contained three polypeptides of 42.5, 44, and 45 kilodaltons (kDa). UV crosslinking of protein to enhancer DNA demonstrated that site C2-binding activities in the three different pools bound DNA through proteins of similar sizes (about 45 kDa), even though the protein-DNA complexes formed by these binding activities were quite distinct. Gel exclusion chromatography and equilibrium binding analyses indicated that the distinct protein-DNA complexes were due to different oligomeric forms of the individual subunits and that a larger multimeric form bound with high affinity to the heavy-chain enhancer site C2, while a smaller species had a much lower affinity for heavy-chain enhancer sequences. Purified protein has been used to map high-affinity binding sites for site C2-binding proteins within an immunoglobulin heavy-chain promoter and at site KE3 in the kappa light-chain enhancer.     

Differential activity of a tissue-specific extinguisher locus in hepatic and nonhepatic cells.

Tissue-specific extinguisher 1 (Tse-1) is a genetic locus on mouse chromosome 11 that can repress expression of several liver genes in trans. This locus is clearly active in fibroblasts, as hepatoma cells retaining fibroblast chromosome 11 are extinguished for both tyrosine aminotransferase and phosphoenolpyruvate carboxykinase gene expression. To assess the activity of Tse-1 in other tissues, we transferred mouse chromosome 11 from several different cell types into rat hepatoma recipients. Tse-1 was active in nonhepatic cell lines derived from each primary germ layer, but Tse-1 activity was not apparent in hybrids between hepatoma cells and primary mouse hepatocytes. These differences in the genetic activity of murine Tse-1 were apparently heritable in cis.     

Early and late effects in the bone marrow of mice following 2 Gy (6 MeV) neutron irradiation

Summary Following 5 Gy gamma irradiation, residual damage in bone marrow persisted up to one year and was ascribed to genetic defects in hemopoietic stem cells (von Wangenheim et al. 1986). To see whether high LET radiation is more efficient in inducing late effects, mice were whole-body irradiated with a single dose of 2 Gy neutrons ( = 6 MeV) and femoral cellularity, CFU-S number, proliferation ability of bone marrow cells (PF) and the compartment ratio (CR), i.e. the splenic 125-iodo-deoxyuridine incorporation per transfused CFU-S were measured up to one year after the radiation insult. Within 12 weeks, femoral cellularity, PF and CR recovered to control or near-control level, whereas CFU-S numbers remained significantly below control. No further recovery was observed. On the contrary, PF and CR deteriorated again after 12 and 26 weeks, respectively. CFU-S per femur tended to decrease as well. Thus it is demonstrated that a single dose of 2 Gy 6 MeV neutrons causes significant injury in function (PF) and structure (CFU-S numbers, CR) of bone marrow which persisted up to one year. While this residual injury can be attributed to genetic defects in hemopoietic stem cells, its increasing expression is probably due to late evolving damage in microenvironmental cells. The RBE of 6 MeV neutrons for the introduction of late effects in the bone marrow is in the range of 3.     

Unusual genetic phenomena associated with Tn5 mutagenesis in Alcaligenes eutrophus strain H1

Tn5 was introduced into Alcaligenes eutrophus strain H1 by a suicide vector pSUP1011. Physical characterization of mutants obtained after Tn5 mutagenesis revealed a relatively high frequency of plasmid curing, or deletion of a 50 kb plasmid DNA segment. Results of Southern hybridization and chromosomal walking indicate that the same continuous stretch of plasmid DNA (designated as D region of plasmid) is deleted in four independent isolates. Moreover, the same deletion of plasmid DNA is also observed in a mitomycin C-generated mutant strain H1-4.Journal Paper No. J-12095 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2607, supported in part by a grant from the Iowa High Technology Council     

Expression and characterization of the tau subunit of phosphorylase kinase

A cDNA encoding the entire tau subunit of rabbit skeletal muscle phosphorylase kinase was reconstructed and inserted into a plasmid containing the Escherichia coli ptac promoter and a constructed plasmid containing the ptac promoter and bacterial chloramphenicol acetyl transferase (CAT) gene, respectively. A significant phosphorylase kinase activity was found, in the first case. In the second case, a fused protein containing 73 amino acids from the CAT protein was obtained. After renaturation, the CAT-tau subunit protein shows enzymatic activity similar to the HPLC-purified and renatured tau subunit.     

Characteristics of children presenting with chest pain to a pediatric emergency department.

Chest pain among children is a common complaint in primary care practice. However, the demographic features and treatment of such patients are controversial. We distributed a questionnaire to 336 consecutive patients with a complaint of chest pain seen during 1 year at an urban pediatric emergency department. Such visits represented 0.6% of all emergency encounters; the male:female ratio was 1.0. Physical examination was done in 325 patients. Chest-wall pain was the most common diagnosis (in 28% of cases). Other causes included pulmonary (in 19%), minor traumatic (in 15%), idiopathic (in 12%) and psychogenic (in 5%); miscellaneous causes (in 21%) most often indicated pain referred from the upper respiratory tract and the abdomen. The most common physical finding was chest tenderness (in 41% of cases). Investigations included chest radiography (in 50% of cases), electrocardiography (in 18%) and determination of the hemoglobin concentration and of the leukocyte count (in 13%); the results were rarely positive. Only eight patients (2%) required admission to hospital, and there were no cases of myocardial ischemia. The findings suggest that health care costs may be reduced by more judicious use of investigations. We conclude that chest pain is an uncommon and usually benign complaint in the pediatric emergency department. Most causes are evident on careful physical examination.