Two mini-F-encoded proteins are essential for equipartition

The par region of mini-F is both necessary and sufficient to promote equipartition of plasmid copies to daughter cells. It is approximately 2.5 kb long and contains the coding sequences for two proteins, F1 (41 kDa) and F2 (37 kDa). We isolated 13 mutants of a phage λ-mini-F hybrid that form unstable plasmids. Two of these putative Par^? mutants are fully suppressible nonsense (amber) mutants. One of the amber mutants, par-41, eliminates the synthesis of F1, generating a large nonsense fragment of the protein. The other mutant, par-36, eliminates the synthesis of F2. Thus both proteins appear to be essential for plasmid equipartition.     

Plasma lipoproteins in Duchenne muscular dystrophy

Plasma lipoproteins of Duchenne muscular dystrophy patients and carriers of the disease, together with age- and sex-matched controls, were examined by density gradient ultracentrifugation and agarose gel electrophoresis. Analysis of density gradient profiles revealed a significant reduction in absorbance (435 nm) by low density and high density lipoproteins from Duchenne patients when compared with controls. Although no abnormalities were observed on electrophoresis of whole plasma samples, the isolated low density lipoprotein fractions from Duchenne patients and carriers displayed increased electrophoretic mobility compared with controls. The results obtained implicate the plasma lipoproteins, in particular the low density lipoproteins, as the primary site of the lesion in this disease.     

Partition of unit-copy miniplasmids to daughter cells. II. The partition region of miniplasmid P1 encodes an essential protein and a centromere-like site at which it acts

The stable maintenance of the unit-copy lambda-P1:5R miniplasmid is dependent on adjacent but separable replication (rep) and partition (par) regions of DNA derived from its P1 plasmid parent. The par region consists of an approximately 2.5 X 10(3) base-pair (kb) segment of DNA of which the terminal kb contains the plasmid incompatibility determinant incB. Two of the 14 lambda-P1:5R partition-defective point mutants isolated are amber (nonsense) mutants, showing that a plasmid-encoded protein is essential for proper partition. All of the Par- point mutants are complemented by the wild-type par region in trans. The complementing activity was shown to be an Mr 44,000 protein encoded by the end of the par region distal to incB. Deletion analysis showed that the incB sequence is essential in cis to the plasmid in order that the plasmid be receptive to the par protein. Thus incB appears to be the target site for par protein activity. We propose that the protein binds to incB, forming a complex that is recognized as a substrate for the cellular partition apparatus. The ability of a cloned incB sequence to compete for the par protein or for the cellular partition apparatus accounts for its activity as an incompatibility determinant. The existence of a plasmid-encoded par protein suggests a specific model for equipartition.     

The effects of haem on translational control of protein synthesis in cell-free extracts from fed and lysine-derived Ehrlich ascites tumour cells

1. Addition of haem to cell-free extracts from Ehrlich ascites tumour cells stimulates protein synthesis only in extracts from cells previously incubated in nutritionally complete conditions. Extracts from amino-acid-deprived cells do not respond to haem. The stimulation of protein synthesis in fed cell extracts is due to increased initiation on endogenous mRNA mediated by an increase in the levels of 40-S-subunit X Met-tRNA initiation complexes. Extracts from starved cells exhibit a defect in 40-S initiation complex formation which cannot be overcome by haem. 2. Experiments to test for the presence of an inhibitor of initiation in Ehrlich cell extracts by monitoring effects on translation in haem-supplemented reticulocyte lysates have revealed that extracts from both fed and starved cells contain one or more inhibitory activities which shut off protein synthesis, dissagregate polysomes and reduce the level of 40-S initiation complexes in the lysate. Extracts from starved cells are more inhibitory for protein synthesis than those from fed cells. 3. Initiation factor eIF-2 is phosphorylated by an endogenous Ehrlich cell protein kinase in vitro, but this occurs to the same extent in extracts from fed and starved cells. 4. We propose a possible model for the role of eIF-2 in the control of protein synthesis by amino acid supply in Ehrlich cells.     

Simple methods for sampling periphyton with observations on sampler design criteria

Requirements for an ideal standard sampling system for defined periphyton communities are discussed. Several simple and inexpensive devices for both spatially discrete and continuous sampling modes are described and field tested in a variety of habitats.     

Hemoglobin Rothschild (β37(C3)Trp → Arg): A high/low affinity hemoglobin mutant

In hemoglobin Rothschild arginine replaces the normal tryptophan at β37(C3), at α₁β₂ contact. Residue β37 is in close proximity to Argα92 (FG4). Substitution of Trp by Arg at β37 results in two positively charged Arg residues at FG4 and C3 facing each other, a situation that would destabilize the subunit constraints essential for the tetrameric integrity of the molecule and for the reduced ligand affinity of unliganded normal HB³ compared to isolated chains.Our studies show liganded HbR is extensively dissociated into dimers and has a high ligand affinity in phosphate buffer and a low ligand affinity in bis-Tris at alkaline pH. Kinetic studies indicate that in the T state HbR has a higher ligand affinity than HbA. This is explained by reduced subunit constraints in the T state and dissociation of the monoliganded species (Hb₄L) into dimers. Kinetic studies also show that R state Hb Rothschild has lower ligand affinity than R state HbA. These results are explained on the basis of extensive dissociation of R state Hb Rothschild into dimers and lower ligand affinity of dimers as compared to triliganded tetramers (α₂β₂(O₂)₃). Kinetic data indicate that the lower ligand affinity of dimers (Hb Rothschild) as compared to that of triliganded tetramers (HbA) is due to the increased ligand dissociation rates in the case of oxyhemoglobin and reduced ligand combination in the case of carboxyderivatives. Both the CO combination reaction time-course around 425 nm and the O₂ dissociation rates at 437.8 nm indicate the presence of large α,β-chain differences in Hb Rothschild.     

Genetic control of the immune response of mice to highly dinitrophenylated human gamma-globulin (DNP56HGG)

The immune response to highly dinitrophenylated human gamma-globulin (DNP56HGG) was tested in inbred strains of mice. Significant differences in the anti-DNP response among inbred strains were found, including the magnitude of serum antibody and the location of plaque-forming cells (spleen or lymph nodes). The strain differences persisted when the dose and adjuvant were changed. The genetic control of the anti-DNP response to DNP56HGG was investigated. The analysis of the response of congenic and F1 hybrid mice to DNP56HGG suggests that at least two genes are involved in the control of the anti-DNP response. The two genes are demonstrated by complementation in the F1 generation, and show no correlation with H-2 haplotype or IgG2a allotype. A third gene may be implicated by differences in response observed between male and female mice.     

Searching for a model for use in vegetation analysis

Summary Indirect gradient analysis methods require an explicit vegetation model which must be based on direct gradient analysis studies. Various vegetation models are reviewed. Field evidence for the models is discussed. Experimental studies of species response to environmental gradients are reviewed and discussed. Three types of gradient are recognized as important for development of models: indirect environmental gradients where the environmental factor has no direct physiological influence on plant growth e.g. elevation; direct environmental gradients where the factor has a direct physiological effect on growth but is not an essential resource, e.g. pH; resource gradients where the factor is an essential resource for plant growth. The behaviour of the ecological carrying capacity and the role of competition along such gradients are shown to be important for developing vegetation models.     

The regeneration of coenzymes using immobilized hydrogenase

Summary A new enzymatic approach to the regeneration of coenzymes has been developed. It uses the reduction of natural or artificial cofactors with H₂, catalyzed by hydrogenase activity in immobilized whole cells ofA. eutrophus. The method has been employed for regeneration of such coenzymes as NAD⁺, FMN, phenazine methosulfate, Janus green, methylene blue, and 2,6-dichlorophenol-indophenol.