Genetic control of flocculation inEscherichia coli

Summary Escherichia coli cells form flocs or aggregates by overproducing type 1 pili. When thepil operon is placed under the control of atac orlac promoter-operator sequence, the bacterial cells can be induced to form flocs by adding isopropyl--d-thiogalactopyranoside to the culture medium. This phenomenon of genetically induced flocculation can aid in the downstream processing of biological products. This paper describes the construction of two artificially controlled plasmids which cause cell flocculation. Cell aggregates 50 m in mean diameter were obtained 1 h after the cells were induced.     

Bacterial plasmids that carry two functional centromere analogs are stable and are partitioned faithfully

The par genes of unit-copy plasmids P1 and F promote equitable distribution of plasmid copies to daughter cells and can be considered to be functional analogs of eucaryotic centromeres. Composite plasmids were constructed which carry either two functional P1 par regions or one F and one P1 region. Unlike dicentric chromosomes, such plasmids are stably maintained.     

Lipid metabolism in rabbits exposed to paraquat aerosol

In order to examine the effects of paraquat on pulmonary lipid metabolism rabbits were exposed to double distilled water by aerosol, or 250 mg paraquat in double distilled water. One hour prior to sacrifice, a group of rabbits were injected with [2?¹⁴C]-acetate. The levels of phospholipids, fatty acids, cholesterol, and triglycerides were determined as were their ¹⁴C-contents in the lung, broncoalveolar lavage fluid, serum, and liver. The serum of paraquat-exposed animals contained significantly increased levels of phospholipids, cholesterol, and triglycerides. Liver, lung, and bronchoalveolar lavage contained less than or equal to control levels of phospholipids, cholesterol, and triglycerides. Percent of palmitate in the hepatic fatty acid profile was slightly increased in liver but not in lung. The source of the increased lipids in the serum is unknown.     

UV inducible UV protection and mutation functions on the I group plasmid TP110

Summary The UV protection and mutation properties of the I group plasmid TP110 have been investigated. It is demonstrated that the genes responsible for these effects are able to complement the deficiency in umuC36 mutants of E. coli, as are the similar genes carried by the B group plasmid R16. Mu-lac inserts into TP110 have been isolated which abolish the UV protection and mutation functions. Restriction mapping of these inserts locates them within a single region of the genome. A comparison of the restriction sites of this region with the muc region of pKM101 reveals very little similarity. Expression of -galactosidase in those Mu-lac inserts in which the lacZ gene is fused to the promoter for the protection and mutation functions is inducible by DNA damaging agents, and induction in mutant strains suggests that these genes are under the direct control of the lexA repressor.     

P1 plasmid replication requires methylated DNA.

Plasmids driven by the plasmid replication origin of bacteriophage P1 cannot be established in Escherichia coli strains that are defective for the DNA adenine methylase (dam). Using a composite plasmid that has two origins, we show that the P1 origin cannot function even in a plasmid that is already established in a dam strain. An in vitro replication system for the P1 origin was developed that uses as a substrate M13 replicative-form DNA containing the minimal P1 origin. The reaction mixture contains a crude extract of E. coli and purified P1 RepA protein. In addition to being RepA dependent, synthesis was shown to be dependent on methylation of the dam methylase-sensitive sites of the substrate DNA. As the P1 origin contains five such sites in a small region known to be critical for origin function, it can be concluded that methylation of these sites is a requirement for initiation. This suggests that the postreplicational methylation of the origin may control reinitiation and contribute to the accuracy of the highly stringent copy-number control of the origin in vivo.     

Advances in the role of minerals in immunobiology

Immunology and our understanding of its various cells, immunoglobulins and lymphokines are recent events that date from the work of Pasteur and Metchnikoff in the late nineteenth century. Experimental evidence has shown the importance of adequate dietary protein and vitamins. The present review examines past and recent experimental evidence for the role of minerals in the functioning of the immune system. Included is in vivo and in vitro information on the macrominerals; calcium and magnesium, the micro-(trace) minerals; iron, zinc, copper, and selenium as they affect various components of the immune system. The effects of gold as either gold-thiomaleate or gold-thioglucose on selenium is also reviewed.     

A refined genetic map of the region of chromosome 17 surrounding the von recklinghausen neurofibromatosis (NF1) gene

The von Recklinghausen neurofibromatosis (NF1) gene has been mapped to the pericentromeric region of chromosome 17. We conducted linkage analyses of NF1 by using 10 polymorphic DNA markers from this chromosomal region. We ascertained 20 American Caucasian NF1 families (163 individuals, 98 NF1 affected) in Michigan and Ohio and also studied a large family ascertained primarily in North Carolina. The following markers were used in this study: HHH202, TH17.19, D17Z1, ERBA1, EW203, EW206, EW207, EW301, CRI-L581, and CRI-L946. NF1 did not recombine with either TH17.19 or HHH202 in any of the informative meioses surveyed (maximum lod scores of 17.04 and 7.21, respectively, at a recombination fraction of .00), indicating that these markers map very close to the NF1 gene. We also report evidence of three instances of recombination between NF1 and the centromeric marker D17Z1 (maximum lod score of 13.43 at a recombination fraction of .04), as well as two crossovers between pairs of marker loci. We find no evidence of locus heterogeneity, and our results support the localization of the NF1 gene to proximal chromosome 17q.     

Absence of mutations in codon 61 of the Ha-ras oncogene in epithelial cells transformed in vitro by 7,12-dimethylbenz(a)anthracene

Epithelial cells of the respiratory tract of rats were transformed in vitro by 7,12-dimethylbenz(a)anthracene (DMBA) which has been reported to cause A----T transversion mutations of the second position of Ha-ras in codon 61 in several biological models. In this study Ha-ras exon 2 was amplified by the polymerase chain reaction (PCR) and then sequenced directly. In 10 transformed cell lines, of which 5 are known to be tumorigenic, no mutations in codon 61 were found. The results suggest that Ha-ras codon 61 mutations are not associated with cell transformation initiated with DMBA in this particular cell transformation system. These data imply that other genes (oncogenes) are responsible for transformation of these cells. The results are discussed in relation to observations in various transformation systems in vivo and in vitro.