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Chargaff's second parity rules for mononucleotides and oligonucleotides (C II mono and C II oligo rules) state that a sufficiently long (>100 kb) strand of genomic DNA that contains N copies of a monoor oligonucleotide, also contains N copies of its reverse complementary mono-or oligonucleotide on the same strand. There is very strong support in the literature for the validity of the rules in coding and noncoding regions, especially for the C II mono rule. Because the experimental support for the C II oligo rule is much less complete, the present article, focusing on the special case of trinucleotides (triplets), examined several gigabases of genome sequences from a wide range of species and kingdoms including organelles such as mitochondria and chloroplasts. I found that all genomes, with the only exception of certain mitochondria, complied with the C II triplet rule at a very high level of accuracy in coding and noncoding regions alike. Based on the growing evidence that genomes may contain up to millions of copies of interspersed repetitive elements, I propose in this article a quantitative formulation of the hypothesis that inversions and inverted transposition could be a major contributing if not dominant factor in the almost universal validity of the rules.chloroplasts ͉ genomics ͉ mitochondria ͉ base composition ͉ oligonucleotide composition

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BEIK cells were inoculated sparsely on one face ("sparse-or s-face") of a thin glass fm whose opposite face was covered with a 2-to 3-day-old confluent layer of BHK cells ("confluent-or c-face"). After 7 hr of attaching and spreading in the absence of visible light, most of the cells on the s-face traversed with their long axes the direction of the whorls of the confluent cells on the c-face directly opposed. The effect was inhibited by a thin metal coating of the glass films. The results suggest that the cells were able to detect the orientation of others by signals that penetrated glass but not thi metallic films and, therefore, appeared to be carried by electromagnetic radiation. In contrast, the effect was not influenced by a thin coat of silicone on the glass, suggesting that the wavelength of this radiation is likely to be in the red to infrared range. The ability of cells to detect the direction of others by electromagnetic signals points to a rudimentary form of cellular "vision."A previous article had suggested among other possibilities that 3T3 cells located and tried to approach distant infrared light sources because they mistook them for other cells (1). If this were true, mammalian tissue cells should be able to detect each other across a partition made of glass.To test this possibility, I studied the behavior of BHK cells that were plated on opposite faces of thin glass films. Cells were plated densely (confluent layer) on one face ("c-face") of the glass film and were allowed to form their typical patterns of whorls. Two days later cells were plated sparsely on the opposite face ("s-face") and were kept in total darkness in a culture incubator for 7 hr while they attached and spread.The cells of the second inoculum did not spread randomly but oriented themselves with respect to the cells directly opposed on the other face ofthe glass film. The present article describes these experiments and others which suggest that the most likely explanation for this phenomenon involves the processing of electromagnetic signals by the cells. MATERIALS AND METHODSGlass Films. The experiments used soda-lime glass substrates with four different levels of thickness. (i) Thin glass films were produced by cutting off the tip of a Pasteur pipette and melting the stump in the flame of a Bunsen burner until it assumed a conical shape. After rapid removal from the flame, the tip was blown into a 6-to 10-cm-diameter balloon by a 1.2-s-long burst of compressed air at 2.5 psi (1 psi = 6.89 kPa). The burst was controlled by a digital time switch (Gralab 451; Thomas Scientific) that opened a solenoid. In areas where the balloon showed strong interference colors, its wall thickness had decreased to <2 pam as determined by scanning electron microscopy with several different samples. These areas of the balloon were broken off, and fragments larger than 5 x 15 mm2 were collected. (ii) Regular glass films came from the other areas of the glass balloon that had wall thicknesses of 6-8 jam as determined by scanning electron ...

Freshly plated 3T3 cells send out radial projections or filopodia. We observed cells which happened to settle on glass near the borderline of a gold-plated area. When some of the filopodia contacted the gold-plated area and others the glass substratum and remained attached for a few minutes, lamellipodia then extended preferentially toward the gold-plated area. 1-2 h later, most of the cells were found in the gold-plated area. When the filopodia of a spreading 3T3 cell contacted another already spread 3T3 cell and also the glass substratum, the first lamellipodia extended preferentially towards the glass. These observations suggest a directionally differentiated extension of lamellipodia after the filopodia of a spreading 3T3 cell have contacted different substrates in their environment. Before filopodia contact a substrate, they perform a rapid "scanning" motion. Therefore, we suggest that the filopodia of a spreading 3T3 cell serve as organs which explore the nonfluid environment and react to a certain quality of the substrate that is presently unknown. Subsequently, they mediate the extension of lameUipodia into the direction in which this quality is found. The described phenomena are reversibly inhibited by Cytochalasin B at concentrations above 5 ~g/ml although filopodia are produced.