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J Hageman

Publications and source records attributed to J Hageman.

15 recordsLinked to original sources
PubMed1994

Methotrexate does not block import of a DHFR fusion protein into chloroplasts.

Protein import into chloroplasts requires the movement of a precursor protein across the envelope membranes. The conformation of a precursor as it passes from the aqueous medium across the hydrophobic membranes is not known in detail. To address this problem we examined precursor conformation during translocation using the chimeric precursor PCDHFR, which contains the plastocyanin (PC) transit peptide in front of mouse cytosolic dihydrofolate reductase (DHFR). The chimeric protein is targeted to chloroplasts and is competent for import. The conformation of PCDHFR can be stabilized by complexing with methotrexate, an analogue of the substrate of DHFR. Methotrexate strongly inhibits DHFR import into yeast mitochondria (M. Eilers and G. Schatz, Nature 322 (1986) 228-232), presumably because the precursor must unfold to cross the membrane and it cannot do so when complexed with methotrexate. We show here that methotrexate does not block PCDHFR import into chloroplasts. Methotrexate does slow the rate of import, and protects DHFR from degradation once inside chloroplasts. The processed protein is localized in the stroma, indicating that import into thylakoids is impeded. Protease sensitivity assays indicate that the complex of precursor protein with methotrexate changes in conformation during the translocation across the envelope.

Amino Acid Sequence↗
PubMed1991

Sex-specific transcriptional regulation of the C. elegans sex-determining gene her-1.

Expression of the sex-determining gene her-1 is required in C. elegans for the normal male development of XO animals. Abnormal expression in XX animals, which normally develop as hermaphrodites, results in aberrant male development. We have isolated a molecular clone of the her-1 gene and have identified two transcripts that are present in XO animals at all stages of development: an abundant 0.8 kb transcript and a less abundant 1.2 kb transcript. In preparations of XX animals, the 0.8 kb transcript was observed only at very low levels in embryos or L1 larvae and the 1.2 kb transcript was not detected. Two gain-of-function her-1 mutations result in high levels of the 1.2 and 0.8 kb transcripts in XX animals. The levels of these transcripts are also elevated in XX animals carrying a loss-of-function mutation in either sdc-1 or sdc-2, consistent with the proposed roles of these genes as negative regulators of her-1. These results demonstrate that expression of the her-1 gene in males and hermaphrodites is controlled at the level of transcript synthesis or accumulation. This mode of regulation contrasts with that found for the Drosophila sex-determining genes, whose sex-specific expression is controlled by differential splicing in males and females.

Animals↗
PubMed1989

Import of proteins into the chloroplast lumen.

Plastocyanin is a nuclear-encoded protein that is functional in the thylakoid lumen of the chloroplast. It is synthesized in the cytoplasm as a precursor with an N-terminal transit peptide of 66 amino acids. Its transport route involves two steps, import into the chloroplasts and subsequent routing over the thylakoid membrane into the lumen. Concomitant with the transport, the transit peptide is removed in two successive steps. The transit peptide consists of two functionally different domains. In this study we examine to what extent each domain is involved in import and routing and how far these two processes are linked. For this purpose we made deletions in the N-terminal and C-terminal part of the transit peptide and fusion proteins which only contain one of these parts. The results show that the N-terminal part of the transit peptide is responsible for import into the chloroplast. The N-terminal 43 amino acids are sufficient to direct other proteins into the stroma. The C-terminal part of the transit peptide is a prerequisite for routing inside the chloroplast but not for import. When deletions are made in this part, the transport of plastocyanin stops after import and the intermediate accumulates in the stroma or on the outside of the thylakoids. Transgenic tomato plants that constitutively express a foreign plastocyanin gene were used to study protein transport in different tissues. Normally, expression of endogenous plastocyanin genes in plants is restricted to photosynthetic tissues only. However, in the transgenic plants this foreign plastocyanin protein is found in all tissues examined. The protein is transported into the local plastids of these tissues and it is processed to the mature size. We conclude that plastids of developmentally different tissues are capable of importing precursor proteins that are normally not found in these tissues. Most likely such plastids, though functionally and morphologically differentiated, have similar or identical protein import mechanisms when compared to the chloroplasts in green tissue. The precursor of ferredoxin was expressed in Escherichia coli. Surprisingly the precursor interacts with the cytoplasmic membrane and is translocated across this membrane. The unprocessed precursor accumulates in the periplasm.

Amino Acid Sequence↗
PubMed1986

The role of the transit peptide in the routing of precursors toward different chloroplast compartments.

The role of the transit peptide in the routing of imported proteins inside the chloroplast was investigated with chimeric proteins in which the transit peptides for the nuclear-encoded ferredoxin and plastocyanin precursors were exchanged. Import and localization experiments with a reconstituted chloroplast system show that the ferredoxin transit peptide directs mature plastocyanin away from its correct location, the thylakoid lumen, to the stroma. With the plastocyanin transit peptide-mature ferredoxin chimera, a processing intermediate is arrested on its way to the lumen. We propose a two domain hypothesis for the plastocyanin transit peptide: the first domain functions in the chloroplast import process, whereas the second is responsible for transport across the thylakoid membrane. Thus, the transit peptide not only targets proteins to the chloroplast, but also is a major determinant in their subsequent localization within the organelle.

Amino Acid Sequence↗
PubMed1986

Clinical correlates do not predict PaO2 response after tolazoline administration in hypoxic newborns.

In an attempt to determine which hypoxic newborns might benefit from administration of tolazoline hydrochloride (Tz), we identified all neonates known to have received Tz at four Chicago area perinatal centers over a 4-yr period. For each of 41 infants, five statistical analyses were used to correlate 31 clinical and ventilatory variables with PaO2 values before and after Tz administration. Fourteen neonates responded to Tz infusion with more than a two-fold increase in PaO2. None of 31 clinical variables successfully predicted a positive Tz response in these infants, and a positive response (increased PaO2) was not associated with increased likelihood of survival. BP fell after Tz in 72% of patients, while heart rate rose after Tz treatment in 66% of cases. These data suggest a need to re-evaluate the administration of Tz to hypoxic newborn infants.

Blood Pressure↗
PubMed1986

Monocyte chemotactic properties in hereditary hemochromatosis.

Several observations indicate that the innate metabolic defect in hereditary hemochromatosis (HH) leads to a defective function of the monocyte-macrophage system. The present study was performed to investigate the possibility that a defect in migration of cells of the monocyte-macrophage system can explain the abnormal location of the submucosal macrophages in HH. Monocytes isolated from 14 patients with HH were investigated with regard to chemotactic responsiveness (MCR). Two different methods were used at two different laboratories. Casein and zymosan-activated serum were used as attractants. No difference in MCR was found between the control group and the group of HH patients. The conclusion can therefore be drawn that the abnormal location of the macrophages of the gut wall in HH cannot be explained by an inborn abnormality of the function of receptors responsible for the chemotactic activity of the monocyte-macrophage system. It is, however, still possible that local factors responsible for the macrophage migration (gut hormones?) may have defective activity in HH patients.

Adult↗
PubMed1985

Transferrin receptors on circulating monocytes in hereditary haemochromatosis.

In patients with hereditary haemochromatosis (HH) abnormal functional properties of the macrophage system have been observed. The present study is a preliminary report of increased transferrin receptor expression on monocytes from 12 patients with HH. There was no correlation between the degree of iron overload and the transferrin receptor expression on the monocytes. The results obtained thus indicate that the observed increase in transferrin receptors is not a secondary phenomenon due to systemic iron overload but could be an expression of a primary inborn error of iron metabolism in HH. The functional aspects of the receptors were not evaluated as they were analyzed by means of monoclonal antibody technique.

Adult↗
PubMed1983

Digital venous subtraction angiography of pulmonary embolism in dogs.

Digital venous subtraction angiography makes it possible to obtain satisfactory images of the pulmonary vessels and thus to evaluate changes in the segmental and subsegmental arteries caused by pulmonary embolism. Morphologic as well as functional images can be produced in the course of a single examination. Semi-quantitative information about the vessels under examination as compared with the corresponding contralateral vessels is thus achieved. This procedure is valuable both in primary diagnosis and in subsequent repeat examinations after treatment.

Angiography↗
PubMed1980

Congenital tuberculosis: critical reappraisal of clinical findings and diagnostic procedures.

The recent pattern of immigration from Indochina and Latin America to the United States suggests that tuberculosis will remain a significant public health problem. Two infants recently seen with probable congenital tuberculosis prompted critical evaluation of the 24 cases of congenital tuberculosis reported in the English literature since the introduction of isoniazid in 1952. Failure to thrive, jaundice, and central nervous system involvement, all reported in previous reviews and textbooks to be very common, were unusual presenting manifestations. In contrast, hepatomegaly, a finding not mentioned in the recent literature, was common. Diagnostic procedures previously underutilized but found in this review to be useful included liver biopsy, biopsy of skin lesions when present, and cultures of gastric aspirates. Factors which enable differentiation of congenital from early postnatally acquired tuberculosis include (1) the presence of known maternal tuberculosis at delivery, (2) whether infant and mother were separated from birth until the onset of illness, and (3) whether other tuberculous exposure of the infant can be determined. Insufficient data prevent recommendation of a preferred regimen of drugs in addition to isoniazid for the treatment of congenital tuberculosis. However, the responses of our patients suggest that streptomycin can be omitted without hazard. Information regarding the long-term prognosis of survivors is lacking, but early diagnosis and institution of appropriate therapy has markedly decreased the mortality of this previously fatal disorder.

Female↗