Light-dependent regulation of the synthesis of soluble and intracytoplasmic membrane proteins of Rhodopseudomonas sphaeroides.

Cells of Rhodopseudomonas sphaeroides grown under saturating light conditions (30 W/m2) and then shifted to low light intensity (3 W/m2) required 2.5 h to adapt to the new lower light conditions. After the shift, cell growth, whole cell protein accumulation, and bacteriochlorophyll accumulation ceased immediately. Approximately midway into the adaptation period, bacteriochlorophyll synthesis commenced at a new, higher rate, which continued through the beginning of the low-light growth period until new steady-state levels were reached. Immediately after the downshift, the rate of cellular protein synthesis declined to 22% of its preshift rate. Pulse-labeling of protein throughout the adaptation period and comparison with a steady-state prelabel culture revealed that synthesis of two of the three light-harvesting proteins, as well as two additional high-molecular-weight photosynthetic membrane proteins, was derepressed three- to fivefold compared with bulk cellular protein. Finally, the synthesis of at least three soluble proteins showed light-dependent regulation after the light downshift. These results are discussed in terms of the light-dependent regulation of synthesis of the photosynthetic membrane macromolecular components and the division of protein synthesis between the photosynthetic membranes and the soluble cell phase.     

The fate of cells with chromosome aberrations after total-body irradiation and bone marrow transplantation

Cytogenetic studies were done on bone marrow cells and peripheral lymphocytes of four patients (three with acute nonlymphocytic leukemia, one with aplastic anemia) at various intervals up to 861 days after total-body X irradiation (TBI) at doses between 4.5 and 10 Gy (450-1000 rad) followed by syngeneic or allogeneic bone marrow transplantation. Whereas no radiation-induced aberrations could be found in the bone marrow, apart from a transient finding in the patient with the lowest radiation dose, aberrant metaphases were seen in the peripheral lymphocytes of three patients in the range from 2.5 to 46% even at 861 days after the exposure. There were no demonstrable aberrations related to TBI in the only patient developing graft-versus-host disease. The dicentric yield as determined in the aberrant metaphases with 46 centromeres ranged between 3.4 +/- 1.3 and 4.9 +/- 0.4. In one patient it was demonstrated by BUdR-labeling that after 10 Gy (1000 rad) TBI the surviving and heavily damaged lymphocytes can go into cell cycle and reach at least the third mitosis. The percentage of aberrant cells diminished by about 25% at each mitotic division.     

Partial characterization and purification of the glycosylation site recognition component of oligosaccharyltransferase

Oligosaccharyltransferase, the enzyme catalyzing the co-translational transfer of oligosaccharide from dolichyl-PP-GlcNAc2Man9Glc3 to -Asn-X-Ser/Thr- sequences in nascent polypeptide chains, was studied in hen oviduct microsomes using the active site-directed photoaffinity probe 125I-labeled N alpha-3-(4-hydroxyphenylpropionyl)-Asn-Lys(N epsilon-p-azidobenzoyl)-Thr-NH2. Several lines of evidence established that the tripeptide probe interacted with a 57-kDa protein of the endoplasmic reticulum that was subsequently glycosylated and converted to a 60-kDa form. The 57-kDa protein, isolated by two-dimensional gel electrophoresis, was used as immunogen to prepare polyclonal antisera. The specificity of the antibody was established on the basis of its ability to 1) recognize the 57-kDa protein by immunoblotting and 2) immunoprecipitate the photolabeled protein. The antibody also recognized photolabeled protein from different tissues and organisms. The 57-kDa protein isolated by immunoprecipitation retained its ability to interact with the photoaffinity probe but was inactive in catalyzing glycosylation of peptides. This result suggests that the 57-kDa protein is the component of oligosaccharyltransferase that recognizes the glycosylation site in polypeptides. These results are discussed in terms of possible models for the structure of oligosaccharyltransferase in the endoplasmic reticulum.     

The effect of vitamin B6 supplements on development of seizures in the gerbil, Meriones unguiculatus.

To see if a Vitamin B6 deficiency is responsible for seizure-proneness in the gerbil, $\text{Meriones unguiculatus}$, a diet supplemented with 0.5mg of pyridoxine per gram of Purina Lab Chow was fed to 8 experimental (E) mated pairs and their litters while 8 control (C) pairs and their litters were fed Purina Lab Chow which contains .004mg per gram of pyridoxine. All litters were tested for seizures every 2 weeks from 2 through 7 mos. of age once a month in a standard (SS) test cage and 2 weeks later in a clean home cage (CC) — and again at 1 yr in the SS cage. There were no differences on any of the measures between E and C litters. Significantly more seizures were elicited in the SS than in the CC tests, and the SS test became increasingly more effective with age. It was concluded that gerbil seizures were not due to a Vitamin B6 deficiency and that some age-related process might be a productive area for future investigation.     

The surgical treatment of necrobiosis lipoidica diabeticorum.

We review the literature on the surgical treatment of necrobiosis lipoidica diabeticorum, and we describe 7 cases treated at Stanford University Medical Center. Experiences with them prompt us to recommend surgical excision of the lesions down to the deep fascia, ligation of the associated perforating blood vessels, and the use of split-skin grafts to cover the defects. There were no recurrences when we did all these things.     

Activation of teratocarcinoma-derived hemoglobin genes in teratocarcinoma-Friend cell hybrids.

Hybrid cells formed by the fusion of murine teratocarcinoma and Friend erythroleukemia cells synthesize hemoglobin in the presence of chemical inducers such as dimethylsulfoxide (DMSO). By making use of the fact that the parental teratocarcinoma and Friend cells carried different alleles at the locus coding for the alpha chain of hemoglobin, it was possible to demonstrate that the teratocarcinoma-derived genes for the globin alpha chains are genetically active in hemoglobin-synthesizing hybrid cells. In addition, evidence is presented suggesting that the teratocarcinoma-derived genes for the beta-globin chains may also be expressed in the hybrids. Apparently the teratocarcinoma-derived genome has become reprogrammed to express erythroid functions following fusion of the teratocarcinoma cell to the Friend cell.