Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Circular code”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources
PubMed1994

Complete nucleotide sequence of a circular plasmid from the Lyme disease spirochete, Borrelia burgdorferi.

We have determined the complete nucleotide sequence of a small circular plasmid from the spirochete Borrelia burgdorferi Ip21, the agent of Lyme disease. The plasmid (cp8.3/Ip21) is 8,303 bp long, has a 76.6% A+T content, and is unstable upon passage of cells in vitro. An analysis of the sequence revealed the presence of two nearly perfect copies of a 184-bp inverted repeat sequence separated by 2,675 bp containing three closely spaced, but nonoverlapping, open reading frames (ORFs). Each inverted repeat ends in sequences that may function as signals for the initiation of transcription and translation of flanking plasmid sequences. A unique oligonucleotide probe based on the repeated sequence showed that the DNA between the repeats is present predominantly in a single orientation. Additional copies of the repeat were not detected elsewhere in the Ip21 genome. An analysis for potential ORFs indicates that the plasmid has nine highly probable protein-coding ORFs and one that is less probable; together, they occupy almost 71% of the nucleotide sequence. Analysis of the deduced amino acid sequences of the ORFs revealed one (ORF-9) with features in common with Borrelia lipoproteins and another (ORF-2) having limited homology with a replication protein, RepC, from a gram-positive plasmid that replicates by a rolling circle (RC) mechanism. Known collectively as RC plasmids, such plasmids require a double-stranded origin at which the Rep protein nicks the DNA to generate a single-stranded replication intermediate. cp8.3/Ip21 has three copies of the heptameric motif characteristically found at a nick site of most RC plasmids. These observations suggest that cp8.3/Ip21 may replicate by an RC mechanism.

Amino Acid Sequence↗
PubMed1998

Human complement factor I: its expression by insect cells and its biochemical and structural characterisation.

Factor I is a five-domain plasma serine protease which is essential for the regulation of the complement system. In order to express this, the factor I coding sequence was cloned into a recombinant baculovirus system, which was used to infect Trichoplusia ni cells. Using the native factor I leader sequence, recombinant factor I (rFI) was secreted into the culture medium. Purified rFI was recognised by polyclonal antisera and by the factor I-specific monoclonal antibody MRC-OX21. SDS PAGE showed that rFI was processed into two chains with molecular weights of 48,000 and 36,000. Amino acid sequence analysis showed that the N-terminal sequences of the rFI chains were the same as those of serum-derived factor I (sFI), confirming that processing was correct. Since both molecular weights were less than those observed for sFI, this is attributed to the replacement of complex-type oligosaccharides by high mannose ones in rFI. C3(NH,) cleavage assays showed that rFI had 55% the activity of sFI. Circular dichroism and Fourier transform infrared spectroscopy showed that the protein folding of rFI and sFI were very similar. Both had a secondary structure low in alpha-helix and high in beta-sheet, as expected from crystal structure and multiple sequence alignment analyses. It is inferred that the reduced activity of rFI is attributable to its changed glycosylation. The availability of rFI and structures for the domains in factor I makes possible new approaches to determine the molecular basis of its interactions with factor H and C3b.

Animals↗
PubMed1996

Selection of potent inhibitors of farnesyl-protein transferase from a synthetic tetrapeptide combinatorial library.

Inhibitors of farnesyl-protein transferase (FPTase) show promise as anticancer agents. Based on the sequence of the protein substrates of FPTase (the CAAX sequence), potent and selective peptidomimetic inhibitors have been developed; these compounds share with the peptide substrate a free thiol and a C-terminal carboxylate. We have used a synthetic tetrapeptide combinatorial library to screen for new leads devoid of these features: the peptides were C-terminally amidated, and no free thiol was included in the combinatorial building blocks. To compensate for this negative bias, an expanded set of 68 amino acids was used, including both L and D as well as many non-coded residues. Sixteen individual tetrapeptides derived from the consensus were synthesized and tested; all were active, showing IC50 values ranging from low micromolar to low nanomolar. The most active peptide, D-tryptophan-D-methionine-D-4-chlorophenylalanine-L-gamma- carboxyglutamic acid (Ki = 2 nM), is also very selective showing little inhibitory activity against the related enzyme geranylgeranyl-protein transferase type I (IC50 > 50 microM). In contrast to CAAX-based peptidomimetics, D-tryptophan-D-methionine-D-4-chlorophenylalanine-L-gamma-carboxyglut amic acid appeared to mimic the isoprenoid substrate farnesyl diphosphate as determined by kinetic and physical measurements. D-Tryptophan-Dmethionine-D-4-chlorophenylalanine-L-gamma- carboxyglutamic acid was a competitive inhibitor of FPTase with respect to farnesyl diphosphate substrate and uncompetitive with respect to CAAX substrate. Furthermore, we demonstrated that FPTase undergoes ligand dependent conformational changes in its circular dichroism spectrum and that D-tryptophan-D-methionine-D-4-chlorophenylalanine-L-gamma- carboxyglutamic acid induced a conformational change identical to that observed with farnesyl diphosphate ligand.

Alkyl and Aryl Transferases↗
PubMed1999

Strain differences in neointimal hyperplasia in the rat.

We performed an initial screen of 11 rat strains by use of a standard balloon injury to the left iliac artery to observe whether genetically determined differences existed in the development of neointimal hyperplasia. Neointimal hyperplasia was assayed 8 weeks after the vascular injury on coded microscopic sections. Statistically significant differences in the percentages of the vascular wall cross-sectional areas composed of intima (percentage intima) secondary to neointimal hyperplasia were noted among the different rat strains (P<0.02), with the Brown-Norway (BN), Dark Agouti, and Milan normotensive strain rats having the highest and the spontaneously hypertensive rats (SHR) having the lowest percentages of intima. In a separate experiment, F1 hybrids of SHRxBN strains and parental BN and SHR underwent the vascular injury, and the parental strains again showed a statistically significant difference from one another in the mean percentage of intima (P<0. 0001). The F1 hybrids showed an average percentage of intima intermediate between those of the parental strains. The average lumen size of the injured BN vessels were significantly smaller than that of the noninjured control vessels (P=0.044), but this significance disappeared when the circular areas of these vessels were calculated without taking neointimal growth into consideration (P=0.649). These results provide the groundwork for a genetic linkage analysis to identify the genes that influence the development of neointimal hyperplasia after vascular injury.

Analysis of Variance↗
PubMed2006

Genome sequence of the chemolithoautotrophic nitrite-oxidizing bacterium Nitrobacter winogradskyi Nb-255.

The alphaproteobacterium Nitrobacter winogradskyi (ATCC 25391) is a gram-negative facultative chemolithoautotroph capable of extracting energy from the oxidation of nitrite to nitrate. Sequencing and analysis of its genome revealed a single circular chromosome of 3,402,093 bp encoding 3,143 predicted proteins. There were extensive similarities to genes in two alphaproteobacteria, Bradyrhizobium japonicum USDA110 (1,300 genes) and Rhodopseudomonas palustris CGA009 CG (815 genes). Genes encoding pathways for known modes of chemolithotrophic and chemoorganotrophic growth were identified. Genes encoding multiple enzymes involved in anapleurotic reactions centered on C2 to C4 metabolism, including a glyoxylate bypass, were annotated. The inability of N. winogradskyi to grow on C6 molecules is consistent with the genome sequence, which lacks genes for complete Embden-Meyerhof and Entner-Doudoroff pathways, and active uptake of sugars. Two gene copies of the nitrite oxidoreductase, type I ribulose-1,5-bisphosphate carboxylase/oxygenase, cytochrome c oxidase, and gene homologs encoding an aerobic-type carbon monoxide dehydrogenase were present. Similarity of nitrite oxidoreductases to respiratory nitrate reductases was confirmed. Approximately 10% of the N. winogradskyi genome codes for genes involved in transport and secretion, including the presence of transporters for various organic-nitrogen molecules. The N. winogradskyi genome provides new insight into the phylogenetic identity and physiological capabilities of nitrite-oxidizing bacteria. The genome will serve as a model to study the cellular and molecular processes that control nitrite oxidation and its interaction with other nitrogen-cycling processes.

Bacterial Proteins↗
PubMed1978

Three species of polyoma virus tumor antigens share common peptides probably near the amino termini of the proteins.

Detergent extracts of polyoma virus-infected mouse cells contain three major proteins of approximately 100,000--108,000 (100K), 55,000 (55K) and 21,500 (22K) daltons, which react with sera obtained from rats carrying tumors induced by the virus. A comparison of the 35S-methionine-, 3H-leucine- and 3H-proline-labeled tryptic peptides of each of these proteins by cation-exchange chromatography followed by descending paper chromatography has shown that: at least five peptides are shared by all three T-reactive proteins; at least three peptides are shared by the 55K and 22K proteins, but not by the 100K protein; at least three peptides are found only in the 22K protein; at least six peptides are found only in the 55K protein; and at least sixteen peptides are found only in the 100K protein. The results are consistent with the hypothesis that the polypeptide chains of the 100K, 55K and 22K dalton tumor antigens of polyoma virus share a common virus-coded amino terminal region. The data also suggest that there is a portion of the polypeptide chains (probably immediately adjacent to the common amino terminal region of the molecules) that is shared by the 55K and 22K proteins, but not by the 100K protein (perhaps because this portion of the genetic information is spliced out of the messenger RNA coding for the 100K protein). The facts that all the peptides common to the 100K and 55K proteins are also found in the 22K protein and are thus assigned to the common amino terminal region of the molecules, and that there are several peptides unique to the 100K protein, as well as several peptides unique to the 55K protein, suggest that the presumed carboxy terminal portion of the polypeptide chain of the 100K protein is considerably, if not entirely, different from that of the 55K protein.

Amino Acid Sequence↗
PubMed1978

Nucleotide sequence of bacteriophage G4 DNA.

The 5,577 nucleotide long sequence of bacteriophage G4 DNA has been determined using the 'plus and minus' and chain termination methods of DNA sequencing. This sequence has been compared with that of the closely related bacteriophage phiX174 (refs 1, 55). In the coding regions there is an average of 33.1% nucleotide sequence differences between the two genomes, but the distribution of these changes is not random and the sequence of some genes is more conserved than others. There is less sequence similarity between the untranslated intergenic regions of G4 and phiX174, but despite this the sequences of the J/F, F/G and H/A untranslated spaces in both genomes have similar sized hairpin loops, which may be related to their function.

Bacteriophages↗
PubMed1994

Identification of catalytically relevant amino acids of the extracellular Serratia marcescens endonuclease by alignment-guided mutagenesis.

By sequence alignment of the extracellular Serratia marcescens nuclease with three related nucleases we have identified seven charged amino acid residues which are conserved in all four sequences. Six of these residues together with four other partially conserved His or Asp residues were changed to alanine by site-directed PCR-mediated mutagenesis using a variant of the nuclease gene in which the coding sequence of the signal peptide was replaced by the coding sequence for an N-terminal affinity tag [Met(His)6GlySer]. Four of the mutant proteins showed almost no reduction in nuclease activity but five displayed a 10- to 1000-fold reduction in activity and one (His110Ala) was inactive. Based upon these results it is suggested that the S.marcescens nuclease employs a mechanism in which His110 acts in concert with a Mg2+ ion and three carboxylates (Asp107, Glu148 and Glu232) as well as one or two basic amino acid residues (Arg108, Arg152).

Amino Acid Sequence↗
PubMed1995

Design, expression, and initial characterization of MB1, a de novo protein enriched in essential amino acids.

Using recently emerging protein folding principles we have designed a protein enriched in the essential amino acids methionine, threonine, lysine and leucine. Our preliminary study of consensus residues (based on charge, hydrophobicity and volume) of natural alpha-helical bundle proteins indicated that the residues M, T, K, and L could be inserted in an alpha-helical bundle structure. We therefore attempted to create a stable de novo protein, highly enriched in these essential amino acids, that would adopt the alpha-helical bundle fold. The design process was an iterative one. The consensus residues (based on the properties profile) for bundle helices were found considering the four helices taken together, helices I to IV individually, or only their N- and C-termini. Using these data, the helices in our de novo protein were designed by inserting the residues M, T, K and L as often as possible at positions where their volume, hydrophobicity and charge match the consensus found in natural bundle helices. Short sequences of strong turn formers were used to join the helices and adjust the predicted p1 to 7.7, while a number of local and global factors were used to refine our design. Further, the sequence was checked to eliminate various known protease targets in E. coli. The sequence of our de novo protein, MB1, is: MAT-EDMTDMMTTLFKTMQLLTK-SEPTA-MDEATKTATTMKNHLQNLMQK-TKNKE DMTDMATTYFKTMQLLTK-TEPSA-MDEATKTATTMKNHLQNLMQK-GVA+ ++ , where dashes separate long helices from short, turn forming linkers. A gene coding for this protein was assembled from synthetic oligonucleotides, then fused to the maltose binding protein gene under the control of a tac promoter. The fusion protein was expressed in E. coli, purified and cleaved to yield maltose binding protein and our de novo protein, MB1. MB1 was found to be helical, to have the expected molecular weight (11 kDa) and the expected content (57%) of the essential amino acids M, T, K and L.

ATP-Binding Cassette Transporters↗
PubMed1992

[Expression of human LSB 32/67 KD gene in E. coli and analysis of its interactions with laminin].

Earlier we have cloned cDNA coding for a polypeptide that reacts with monoclonal antibodies specific for some cytoskeleton structures. This gene is homologous to the laminin receptor 67 KD. However, cDNA suffices only for a polypeptide of 32 Da, far smaller than the 67 rDa laminin receptor. We have constructed a vector that produces the fusion protein LBP-TrpE in the bacterial strain CAG-456. Our studies show that hybrid protein LBP-TrpE is able to interact with laminin. This result was confirmed by using following methods: immunoblotting, "ELISA" and affinity chromatography on laminin.

Amino Acid Sequence↗
PubMed1998

Molecular and immunologic characterization of a highly cross-reactive two EF-hand calcium-binding alder pollen allergen, Aln g 4: structural basis for calcium-modulated IgE recognition.

Serum IgE was used to isolate a cDNA coding for a 9.4-kDa two EF-hand calcium-binding allergen, Aln g 4, from a lambda gt11 expression cDNA library constructed from alder (Alnus glutinosa) pollen. rAln g 4 was overexpressed in Escherichia coli and purified to homogeneity. It reacted with serum IgE from 18% of pollen-allergic patients (n = 122); shared IgE epitopes with homologous allergens present in tree, grass, and weed pollens; and thus belongs to a family of highly cross-reactive pollen allergens. Exposure of two E. coli-expressed rAln g 4 fragments comprising amino acids 1-41 and 42-85 to patients' IgE Abs, as well as to a rabbit antiserum raised against purified rAln g 4, indicated that most of the B cell epitopes reside in the N-terminal portion of the protein. IgE recognition of Aln g 4 was strongly modulated by the presence or absence of calcium. Circular dichroism analysis of rAln g 4 revealed that the protein consisted mostly of alpha helical secondary structure and possessed a remarkable thermal stability and refolding capacity, a property that was greatly reduced after calcium depletion. Circular dichroism analysis of the calcium-bound and apo form of rAln g 4 indicated that calcium-induced modulation of IgE binding could be due to changes in the protein conformation. Purified rAln g 4 elicited dose-dependent basophil histamine release and immediate type skin reactions in sensitized patients. It may hence be useful for allergy diagnosis and for specific immunotherapy.

Allergens↗
PubMed2004

Movement-related and preparatory activity in the reticulospinal system of the monkey.

Three monkeys ( M. fascicularis) performed a center-out, two-dimensional reaching task that included an instructed delay interval based on a color-coded visuospatial cue. Neural activity in the medial pontomedullary reticular formation (mPMRF) was recorded along with hand movement. Of 176 neurons with movement-related activity, 109 (62%) had movement-related but not preparatory activity (M cells), and 67 (38%) had both movement-related and preparatory activity (MP cells). EOG analyses indicated that the preparatory activity was not consistent with control of eye movements. There were slight changes in electromyograms (EMG) late in the instructed delay period before the Go cue, but these were small compared with the movement-related EMG activity. Preparatory activity, like the EMG activity, was also confined to the end of the instructed delay period for 14 MP cells, but the remaining 53 MP cells (30%) had preparatory activity that was not reflected in the EMG. Peri-movement neural activity varied with movement direction for 70% of the cells, but this variation rarely fit circular statistics commonly used for studies of directional tuning; directional tuning was even less common in the preparatory activity. These data show that neurons in the mPMRF are strongly modulated during small reaching movements, but this modulation was rarely correlated with the trajectory of the hand. In accord with findings in the literature from other regions of the CNS, evidence of activity related to motor preparation in these cells indicates that this function is distributed in the nervous system and is not a feature limited to the cerebral cortex.

Action Potentials↗
PubMed1989

Purification of receptor protein Trg by exploiting a property common to chemotactic transducers of Escherichia coli.

The methyl-accepting chemotactic transducers of Escherichia coli were found to bind strongly to Cibacron blue-Sepharose. Among potential elutants tested, only S-adenosylmethionine at moderate concentrations and NaCl at concentrations greater than 1.5 M caused dissociation of these detergent-solubilized transmembrane proteins from the dye. Release by S-adenosylmethionine may be a generalized effect rather than the result of a specific binding site for that compound on transducers. A truncated trg gene was created that coded for the carboxyl-terminal three-fifths of the transducer, which constitutes the cytoplasmic domain common to all four transducers in E. coli. This domain bound to Cibacron blue-Sepharose and was eluted in a pattern similar to that exhibited by intact Trg, indicating that interaction with the dye occurred in this conserved domain. Adherence to Cibacron blue and elution by high salt formed the core of an efficient purification scheme, developed for Trg but applicable to all transducers in E. coli and perhaps to methyl-accepting chemotaxis proteins in other species. Determination of the amino acid sequence at the beginning of purified Trg confirmed that it contained a longer hydrophilic segment at its amino terminus than other transducers of E. coli. The initial methionine of Trg is neither cleaved nor modified, in contrast to the Tar transducer in which the amino terminus was found previously to be blocked. Circular dichroic measurements of purified Trg indicated that the secondary structural organization of the protein is predominantly alpha-helix.

Amino Acids↗
PubMed2001

Progress and challenges in the theory and interpretation of X-ray spectra.

There has been dramatic progress over the past decade both in theory and in ab initio calculations of X-ray absorption fine structure (XAFS). Rapid progress is now being made in understanding X-ray absorption near-edge structure (XANES). This presentation reviews the developments in this field by many groups leading up to the current state of the art. These developments have led to several ab initio codes, such as FEFF, which yield results comparable to experimental results for XAFS, and permit an interpretation of the spectra in terms of geometrical and electronic properties of a material. The review begins with a summary of the key theoretical developments that are essential for achieving a quantitative agreement with experiment for XAFS. The same high-order multiple-scattering (MS) theory of XAFS can also give an approximate treatment of XANES, but this approach can fail close to an edge, where full MS calculations are often necessary. However, a fully quantitative treatment of XANES remains challenging, largely as a result of a number of many-body effects, e.g. the approximate treatment of the core-hole, multiplet effects, the photoelectron self energy and inelastic losses. Finally, natural extensions of the theory to other spectroscopies, such as anomalous X-ray scattering, DAFS (diffraction anomalous fine structure) and XMCD (X-ray magnetic circular dichroism) are briefly discussed. These developments are illustrated with a number of applications.

Journal Article↗
PubMed2002

oriC region and replication termination site, dif, of the Xanthomonas campestris pv. campestris 17 chromosome.

A 13-kb DNA fragment containing oriC and the flanking genes thdF, orf900, yidC, rnpA, rpmH, oriC, dnaA, dnaN, recF, and gyrB was cloned from the gram-negative plant pathogen Xanthomonas campestris pv. campestris 17. These genes are conserved in order with other eubacterial oriC genes and code for proteins that share high degrees of identity with their homologues, except for orf900, which has a homologue only in Xylella fastidiosa. The dnaA/dnaN intergenic region (273 bp) identified to be the minimal oriC region responsible for autonomous replication has 10 pure AT clusters of four to seven bases and only three consensus DnaA boxes. These findings are in disagreement with the notion that typical oriCs contain four or more DnaA boxes located upstream of the dnaA gene. The X. campestris pv. campestris 17 attB site required for site-specific integration of cloned fragments from filamentous phage phiLf replicative form DNA was identified to be a dif site on the basis of similarities in nucleotide sequence and function with the Escherichia coli dif site required for chromosome dimer resolution and whose deletion causes filamentation of the cells. The oriC and dif sites were located at 12:00 and 6:00, respectively, on the circular X. campestris pv. campestris 17 chromosome map, similar to the locations found for E. coli sites. Computer searches revealed the presence of both the dif site and XerC/XerD recombinase homologues in 16 of the 42 fully sequenced eubacterial genomes, but eight of the dif sites are located far away from the 6:00 point instead of being placed opposite the cognate oriC. The differences in the relative position suggest that mechanisms different from that of E. coli may participate in the control of chromosome replication.

Amino Acid Sequence↗
PubMed1982

Sequence homology and recombination between the genomes of morphologically dissimilar bacteriophages LP 52 and theta.

A restriction fragment map of Bacillus licheniformis temperate phage LP 52 DNA (molecular weight 38.5 X 10(6)) was established, using restriction endonucleases BamHI (8 target sites), BglI (10 sites,) BglII (13 sites) and EcoRI (22 sites). The map is linear, with well-defined ends, without any signs of circular permutation. The DNA of a related phage, LP 51, produced identical restriction fragments. At least 62% DNA of LP 52 has been found homologous to the DNA of the recently discovered, morphologically quite dissimilar, phage I, as demonstrated by hybridization of electrophoretically separated restriction fragments of DNA. Under the same conditions, the DNAs of LP 52 and of the morphologically similar Bacillus subtilis phage phi 105 did not cross-hybridize. The homologous regions in the genomes of phages LP 52 and I have been shown to be colinear. Comparison of the cleavage maps of phages LP 52 and I has shown that, within the regions of homology, not a single restriction fragment and few restriction sites have been conserved during divergent evolution. Three major regions of heterology were defined; the longest one, covering the right-hand end of the map (73 +/- 2.75% up to 100% LP 52 genome length) appeared to contain genes coding for structural proteins of the virions; a shorter region at the left-hand end of the map (coordinates zero to 10.3 +/- 3.3% LP 52 genome length) and a very short central region (coordinates 41.8-43.9%) could be identified, the latter apparently containing a regulatory locus responsible for the heteroimmune behavior of the two phages. Recombinants between phages LP 52 and I were isolated. Mapping of recombinant genomes has indicated mutual substitution of allelic pieces of LP 52 and I DNAs upon strict conservation of overall genome length.

Bacteriophages↗
PubMed1995

Recent developments in the molecular biology of anaplasmosis.

Recent applications of DNA analysis, cloning, sequencing and expression technology have resulted in significant advances in our understanding of the hemoparasite Anaplasma marginale. Analysis of 16S ribosomal RNA has confirmed a phylogenetic position close to Ehrlichia sp. and Cowdria ruminantium. Intact genomic DNA of A. marginale digested with SfiI separates into bands from 14 to 170 kbp on pulse-field gels, with a total genome size of 1200-1260 kbp and G + C content of 56 mol%. Major surface proteins (MSP1-MSP5) have been identified and DNA coding sequences are available for most of these. These data have revealed that MSPs may be quite polymorphic between different geographic isolates, may be encoded by multi-gene families, and have some similar features to other prokaryotes including signal peptidase cleavage sites and gene regulatory sequences. Homologies have been detected between MSPs and immunodominant proteins of Cowdria ruminantium. Several MSPs have been expressed to high level and purified from recombinant Escherichia coli. MSP 1, 2 and 4 have potential for the development of vaccines and MSP3 and 5 for improved diagnostic assays.

Anaplasma↗
PubMed2000

Which retinal and extra-retinal information is crucial for circular vection?

In contradistinction to conventional wisdom, we propose that retinal image slip of a visual scene (optokinetic pattern, OP) does not constitute the only crucial input for visually induced percepts of self-motion (vection). Instead, the hypothesis is investigated that there are three input factors: 1) OP retinal image slip, 2) motion of the ocular orbital shadows across the retinae, and 3) smooth pursuit eye movements (efference copy). To test this hypothesis, we visually induced percepts of sinusoidal rotatory self-motion (circular vection, CV) in the absence of vestibular stimulation. Subjects were presented with three concurrent stimuli: a large visual OP, a fixation point to be pursued with the eyes (both projected in superposition on a semi-circular screen), and a dark window frame placed close to the eyes to create artificial visual field boundaries that simulate ocular orbital rim boundary shadows, but which could be moved across the retinae independent from eye movements. In different combinations these stimuli were independently moved or kept stationary. When moved together (horizontally and sinusoidally around the subject's head), they did so in precise temporal synchrony at 0.05 Hz. The results show that the occurrence of CV requires retinal slip of the OP and/or relative motion between the orbital boundary shadows and the OP. On the other hand, CV does not develop when the two retinal slip signals equal each other (no relative motion) and concur with pursuit eye movements (as it is the case, e.g., when we follow with the eyes the motion of a target on a stationary visual scene). The findings were formalized in terms of a simulation model. In the model two signals coding relative motion between OP and head are fused and fed into the mechanism for CV, a visuo-oculomotor one, derived from OP retinal slip and eye movement efference copy, and a purely visual signal of relative motion between the orbital rims (head) and the OP. The latter signal is also used, together with a version of the oculomotor efference copy, for a mechanism that suppresses CV at a later stage of processing in conditions in which the retinal slip signals are self-generated by smooth pursuit eye movements.

Adult↗