Changes of Escherichia coli cell cycle parameters during fast growth and throughout growth with limiting amounts of thymine

It is generally accepted that during fast growth of Escherichia coli, the time (D) between the end of a round of DNA replication and cell division is constant. This concept is not consistent with the fact that average cell mass of a culture is an exponential function of the growth rate, if it is also accepted that average cell mass per origin of DNA replication (M_i) changes with growth rate and negative exponential cell age distribution is taken into account. Data obtained from cell composition analysis of E. coli OV-2 have shown that not only (M_i) but also D varied with growth rate at generation times () between 54 and 30 min. E. coli OV-2 is a thymine auxotroph in which the replication time (C) can be lengthened, without inducing changes in , by growth with limiting amounts of thymine. This property has been used to study the relationship between cell size and division from cell composition measurements during growth with different amounts of thymine. When C increased, average cell mass at the end of a round of DNA replication also increased while D decreased, but only the time lapse (d) between the end of a replication round and cell constriction initiation appeared to be affected because the constriction period remained fairly constant. We propose that the rate at which cells proceed to constriction initiation from the end of replication is regulated by cell mass at this event, big cells having shorter d times than small cells.Abbreviations OD₄₅₀ and OD₆₃₀ Optical density at a given wavelength in nm Dedicated to Dr. John Ingraham to honor him for his many contributions to Science     

On the solution of mathematical models of herd immunity in human helminth infections

The general solution of the mathematical model of herd immunity to human helminth infections recently proposed by Anderson and May [3] is obtained. The numerical solution of a more accurate biological model is indistinguishable from the corresponding exact solution of a more tractable mathematical model. Computer simulations of some particular cases of this model support the notion that both ecological and immunological factors determine the observed convex patterns of age-prevalence and age-intensity curves of human helminth infections.This work was made thanks to the advise and support of Dr. Robert M. May while the author was Postdoctoral Fellow at Princeton University     

Transformation of NIH 3T3 cells by overexpression of the normal coding sequence of the rat neu gene.

While the normal human erbB-2 gene is potently transforming when overexpressed in NIH 3T3 cells, its rat homolog, the neu gene, seems to acquire transforming properties only upon alteration of its coding sequence. In this study, we compared the effects of different levels of expression of normal erbB-2 and neu in NIH 3T3 cells. Our results revealed that the normal rat neu gene acts as a potent oncogene when sufficiently overexpressed in NIH 3T3 cells.     

Expression of HOX homeogenes in human neuroblastoma cell culture lines

Mammalian genes containing a class-I homeobox (HOX genes) are highly expressed in the embryonic nervous system. As a first step towards the molecular analysis of the role these genes play in neural cells, we studied the expression of four human HOX genes in five neuroblastoma (NB) cell lines - SK-N-BE, CHP-134, IMR-32, SK-N-SH and LAN-1 - during the process of differentiation induced by treatment with retinoic acid (RA). The four genes, HOX1D, 2F, 3E and 4B, located at corresponding positions in the four HOX loci, share a high degree of sequence similarity with the Drosophila Deformed homeotic gene and constitute a homology group, group 10. One of these genes, HOX1D, is not expressed in the cells used, whereas the other three are highly expressed in untreated and RA-induced NB cells, even though the expression pattern in the various lines is slightly different for the three genes. Our analysis reveals a complex and specific expression pattern in these lines, paving the way to an identification of different NB-cell populations by means of specific HOX gene expression schemes. On the other hand, in every line studied, morphological maturation toward a neuronal differentiated phenotype appears to be associated with increased HOX gene expression.     

Cathepsin B secretion by rabbit articular chondrocytes: modulation by cycloheximide and glycosaminoglycans

Rabbit articular chondrocytes in monolayer culture are modulated away from their differentiated state and undergo morphological and biochemical changes. One of the characteristics of the modulated state is an abnormally high production of the cysteine endopeptidase cathepsin B. Addition to chondrocyte cultures of the protein biosynthesis inhibitor, cycloheximide, resulted in a concentration-dependent reduction of cathepsin B secretion, which was fully restored after removal of cycloheximide. Glycosaminoglycans added to the culture medium of modulated chondrocytes partially reduced the rate of secretion of cathepsin B, this effect being dependent on their structure, the degree of sulfation, and concentration. The age of the chondrocytes and the duration of the treatment also influenced this response. The switching off of cathepsin B release was apparently best favored by a high concentration of negatively charged sulfate groups attached to a polymeric glycosaminoglycan chain; this simulates the natural environment of the chondrocytes in articular cartilage.     

Immunological studies of ferredoxin-nitrite reductases and ferredoxin-glutamate synthases from photosynthetic organisms

Polyclonal antiserum specific for ferredoxin-nitrite reductase (EC 1.7.7.1) from the green alga Chlamydomonas reinhardii recognized the nitrite reductase from other green algae, but did not cross-react with the corresponding enzyme from different cyanobacteria or higher plant leaves. An analogous situation was also found for ferredoxin-glutamate synthase (EC 1.4.7.1), using its specific antiserum. Besides, the antibodies raised against C. reinhardii ferredoxin-glutamate synthase were able to inactivate the ferredoxin-dependent activity of nitrite reductase from green algae.These results suggest that there exist similar domains in ferredoxin-nitrite reductases and ferredoxin-glutamate synthases from green algae. In addition, both types of enzymes share common antigenic determinants, probably located at the ferredoxin-binding domain. In spite of their physicochemical resemblances, no apparent antigenic correlation exists between the corresponding enzymes from green algae and those from higher plant leaves or cyanobacteria.Abbreviations Fd ferredoxin - GOGAT glutamate synthase - MV⁺ reduced methyl viologen (radical cation) - NiR nitrite reductase - PMSF phenylmethylsulphonyl fluoride - SDS sodium dodecyl sulfate     

Combination treatment using thymosin α1 and interferon after cyclophosphamide is able to cure Lewis lung carcinoma in mice

Summary A combination treatment with thymosin 1 (200 µg/kg) for 4 days, followed by a single injection of murine interferon / (3 × 10⁴ international units/mouse), starting 2 days after cyclophosphamide treatment (200 mg/kg, single injection) demonstrated a dramatic and rapid disappearance of tumor burden in mice bearing Lewis lung carcinoma (3LL) tumor. The effectiveness of this new chemoimmunotherapy protocol was evident even on the long-term survival in a high percentage of animals, and was statistically significant when compared to treatment with the single agents in conjunction with chemotherapy or to chemotherapy itself. The same combination immunotherapy treatment strongly stimulated natural killer activity and cytotoxicity against autologus 3LL tumor cells in 3LL-tumor-bearing mice treated with cyclophosphamide, whereas treatments with each agent singly did not alter or only slightly modified the cytotoxic activity towards Yac-1 or 3LL target cells. Selective depletion with antibodies showed that killer cells stimulated by combination chemoimmunotherapy treatment bear phenotypic characteristics of asialo-GM1-positive cells. A histological study has shown a high number of infiltrating lymphoid cells in the tumors obtained from mice treated with combination chemoimmunotherapy.     

Transposon-generated Tn10 insertion mutations at thearo genes ofEscherichia coli K-12

We have obtained a set ofEscherichia coli K-12 derivatives with transposon-generated Tn10 insertion mutations at thearo genes of their aromatic biosynthetic pathway. Bacteriophage NK561 (Tn10) has been used for transposon mutagenesis ofE. coli, strain BW545. Tetracycline (Tc)-resistant derivatives were screened by their Aro^– phenotype by growth on a minimal medium with adequate requirements. Sixaro mutant types were mapped; two strains werearoA, twoaroD, onearoB oraroE, and onearoC. A selective medium and ad-cycloserine enrichment in the presence of tetracycline were used to select for Aro^–, Tc-sensitive derivatives. The reversion index to aromatic-independent colonies of some derivatives was less than 2 × 10^–11 per bacterium per generation. P1 transduction experiments transferred an aroA::Tn10 insertion fromE. coli BW545 to an enterotoxigenicE. coli strain from porcine origin. Derivatives of this strain beingaro, Tc-sensitive and not reverting toaro ⁺ at a detectable frequency, and many others transduced at will, may prove their usefulness as live vaccines.     

Indole-3-acetic acid content and glutamine synthetase activity in the pericarp, and peroxidase activity and isoenzymes in the meso- and exocarp of growing peach fruits

The indole-3-acetic acid (IAA) content in peach pericarp (Prunus persica L. Batsch cv. Merry) was highest at early stage I of development (200 ng/g fresh wt), decreased to the lowest level during stage II, and rose again at stage III to 60–70 ng/g fresh wt. High activity of glutamine synthetase was found in the pericarp during stage I. The soluble peroxidase activity was highest in the meso- and exocarp at stage II, and isoenzymatic changes in this fraction corresponded to the transition from cationic isoenzymes, predominant at stage I, to anionic isoenzymes at stage III. The ionically bound peroxidase activity in these tissues was highest at stage I. The three developmental stages showed marked differences in auxin content and enzyme activities; for peroxidases these changes reflect a developmental expression pattern for the isoenzymes.