The relation between the synergistic effect of cytostatics and metabolism of V 79B cells in vitro.

A single-dose simultaneous application of methotrexate (MTX; 0.002/microgram ml-1) and cisplatin (cis-Pt; 0.0002/microgram ml-1) had a permanent synergistic effect on both synchronized and asynchronous cell populations of V 79B cells. Successive combination of the drugs was manifested synergistically when MTX was applied first. The synchronized cell population was more sensitive to the cytostatics than the asynchronous population. Treatment with MTX alone, or the combination of MTX-cis-Pt, as well as their successive combination with the first drug being cis-Pt, caused gluconeogenesis.     

Molecular basis of variegate porphyria: a de novo insertion mutation in the protoporphyrinogen oxidase gene

The porphyrias are disorders that result from the inherited or acquired dysregulation of one of the eight enzymes in the heme biosynthetic pathway. Variegate porphyria (VP) is characterized by deficiencies in protoporphyrinogen oxidase (PPO) and has recently been genetically linked (Z = 6.62) to the PPO gene on chromosome 1q21. In this study, we have identified two sequence variants in the PPO gene in a family with VP. The first is a neutral polymorphism at the -47 position of intron 2; this polymorphism is present in the general population and is unlikely to underlie the VP phenotype. The second is a mutation in the PPO gene in a patient with VP; the mutation consists of an apparently de novo 2-bp insertion in exon 3 of PPO and results in a frameshift and downstream premature termination codon. These data establish that a frameshift mutation in PPO is the underlying mutation in this patient with VP and explain the sporadic occurrence of the phenotype in this family. Received: 29 May 1996 / Revised: 20 August 1996     

The proto-Nucleic Acid Builder: a software tool for constructing nucleic acid analogs

The helical structures of DNA and RNA were originally revealed by experimental data. Likewise, the development of programs for modeling these natural polymers was guided by known structures. These nucleic acid polymers represent only two members of a potentially vast class of polymers with similar structural features, but that differ from DNA and RNA in the backbone or nucleobases. Xeno nucleic acids (XNAs) incorporate alternative backbones that affect the conformational, chemical, and thermodynamic properties of XNAs. Given the vast chemical space of possible XNAs, computational modeling of alternative nucleic acids can accelerate the search for plausible nucleic acid analogs and guide their rational design. Additionally, a tool for the modeling of nucleic acids could help reveal what nucleic acid polymers may have existed before RNA in the early evolution of life. To aid the development of novel XNA polymers and the search for possible pre-RNA candidates, this article presents the proto-Nucleic Acid Builder (https://github.com/GT-NucleicAcids/pnab), an open-source program for modeling nucleic acid analogs with alternative backbones and nucleobases. The torsion-driven conformation search procedure implemented here predicts structures with good accuracy compared to experimental structures, and correctly demonstrates the correlation between the helical structure and the backbone conformation in DNA and RNA.     

The role of the fibrillar component of the surface sheath in the morphogenesis of Dictyostelium discoideum

We have isolated a fibrillar component of the surface sheath of Dictyostelium discoideum by virtue of its insolubility in 9 M urea-2% sodium dodecyl sulfate (US). The US-insoluble material is primarily composed of cellulose, but also contains other carbohydrate components, protein, and lipid. Evidence is presented that the US-insoluble material is a component of the sheath. Sheath isolated from mutant strains lacking the developmentally regulated N-acetylglucosaminidase (NAG), α-mannosidase, or β-glucosidase activities is similar in composition to sheath isolated from wildtype strain. Strains lacking NAG are unable to migrate normally. This may result from the markedly lower crystallinity of the cellulose in the US-insoluble sheath isolated from these mutants. Strains lacking α-mannosidase or β-glucosidase migrate normally and the crystallinity of the sheath cellulose is not significantly below that of the wildtype. The correlation between the lower crystallinity of cellulose and the inability of strains lacking NAG to migrate suggests that crystallinity is physiologically important and that the degree of crystallinity is controlled by an enzymatic, mutable process. Strains U1 and UN1, which have <1% of the wildtype activity of uridine diphosphate glucose pyrophosphorylase activity, develop in a morphologically normal fashion to the slug stage. However, they cannot form stalk or spore cells, nor can they produce cellulose. These strains do not produce any detectable US-insoluble sheath and are fragile and unable to migrate. A continuous, nonfibrillar sheath surrounds the aggregates and is sufficient for normal morphogenesis up to the slug stage. The fibrillar component gives the aggregate the added rigidity required during migration.