The tetrahymena ribozyme cleaves a 5'-methylene phosphonate monoester approximately 10(2)-fold faster than a normal phosphate diester: implications for enzyme catalysis of phosphoryl transfer reactions.

Single-atom substrate modifications have revealed an intricate network of transition state interactions in the Tetrahymena ribozyme reaction. So far, these studies have targeted virtually every oxygen atom near the reaction center, except one, the 5'-bridging oxygen atom of the scissile phosphate. To address whether interactions with this atom play any role in catalysis, we used a new type of DNA substrate in which the 5'-oxygen is replaced with a methylene (-CH2-) unit. Under (kcat/Km)S conditions, the methylene phosphonate monoester substrate dCCCUCUT(mp)TA4 (where mp indicates the position of the phosphonate linkage) unexpectedly reacts approximately 10(3)-fold faster than the analogous control substrates lacking the -CH2- modification. Experiments with DNA-RNA chimeric substrates reveal that the -CH2- modification enhances docking of the substrates into the catalytic core of the ribozyme by approximately 10-fold and stimulates the chemical cleavage by approximately 10(2)-fold. The docking effect apparently arises from the ability of the -CH2- unit to suppress inherently deleterious effects caused by the thymidine residue that immediately follows the cleavage site. To analyze the -O- to -CH2- modification in the absence of this thymidine residue, we prepared oligonucleotide substrates containing methyl phosphate or ethyl phosphonate at the reaction center, thereby eliminating the 3'-terminal TA4 nucleotidyl group. In this context, the -O- to -CH2-modification has no effect on docking but retains the approximately 10(2)-fold effect on the chemical step. To investigate further the stimulatory influence on the chemical step, we measured the "intrinsic" effect of the -O- to -CH2- modification in nonenzymatic reactions with nucleophiles. We found that in solution, the -CH2- modification stimulates chemical reactivity of the phosphorus center by <5-fold, substantially lower in magnitude than the stimulatory effect in the catalytic core of the ribozyme. The greater stimulatory effect of the -CH2- modification in the active site compared to in solution may arise from fortuitous changes in molecular geometry that allow the ribozyme to accommodate the phosphonate transition state better than the natural phosphodiester transition state. As the -CH2- unit lacks lone pair electrons, its effectiveness in the ribozyme reaction suggests that the 5'-oxygen of the scissile phosphate plays no role in catalysis via hydrogen bonding or metal ion coordination. Finally, we show by analysis of physical organic data that such interactions in general provide little catalytic advantage to RNA and protein phosphoryl transferases because the 5'-oxygen undergoes only a small buildup of negative charge during the reaction. In addition to its mechanistic significance for the Tetrahymena ribozyme reaction and phosphoryl transfer reactions in general, this work suggests that phosphonate monoesters may provide a novel molecular tool for determining whether the chemical step limits the rate of an enzymatic reaction. As methylene phosphonate monoesters react modestly faster than phosphate diesters in model reactions, a similarly modest stimulatory effect on an enzymatic reaction upon -CH2- substitution would suggest rate-limiting chemistry.

A computerized visual-search task as a measure of cerebral dysfunction and organization.

This study examined differences in performance on a visual-search task between dysphonetic dyslexic children and three other groups of youngsters (other dyslexic, brain-damaged, and normals) on measures of cerebral dysfunction and cerebral organization. Subjects were required to match a centrally located design to an identical image, yielding a measure of cerebral dysfunction, i.e., latency. Cerebral organization of the diagnostic groups was studied by measuring the conjugate lateral eye movements of each child. Prior research suggests that initial direction of lateral eye movement on a cognitive task is indicative of lateralized cerebral activation. Analysis indicated that the dysphonetic dyslexics group, as predicted, differed significantly on latency from the normal and brain-damaged groups but not from the other dyslexic group. The dysphonetic dyslexic group differed significantly from all other groups on the measure of cerebral organization.

False negatives, Canter's Background Interference Procedure, the trail making test, and epileptics.

This study correlated the Canter's Background Interference Procedure (BIP) scores of 141 adult epileptics with the five variables of age at onset of symptoms, etiology, type of symptoms, severity of generalized background dysrhythmia, and locus of lesion. These variables did not correlate significantly with the BIP scores, contrary to expectations. The BIP's nearly 50% false negative rate was much higher than that of the Trail Making Test, using either Reitan's or Russell's cutting scores for Trails A (33% and 21%, respectively) or Trails B (35% and 28.5%, respectively). The BIP often does not agree with abnormal neurological diagnoses, but often does agree with psychiatric diagnoses of Organic Brain Syndrome (OBS). The authors argue that this is due to the BIP's normative history and to its sensitivity to organic concreteness. The authors suggest that future BIP validity studies include a behavioral measure of OBS as criterion.

Sensory process instruction with learning disabled children.

To determine whether the use of a teaching method geared to an individual learner's dominant perceptual modality would increase level of learning and the efficiency with which that level was achieved on a selected learning task 60 children (8 to 12 yr. old) were divided into three groups of 20 each based upon performance on two perceptual screening procedures. In the instructional phase the subject was given information to be mastered under the following three sensory modalities, Auditory-Vocal-Motor, a Visual-Vocal-Motor, and Combination channel. A two-way analysis of variance yielded significant main effects for training in the visual and combined conditions only.

Reversed memory coding and symbol reversal in children.

The present study examined an hypothesized mirror-reversed memory-coding phenomenon whereby aligned and mirror-reversed memory records in opposite cerebral hemispheres are confused. Two groups of 7-yr.-old boys were chosen on the basis of tendency to confuse mirror and aligned written symbols. The experimental task required discrimination as same or different of letter pairs which were either same or different and either aligned or mirror-reversed. The pairs were simultaneously presented to right, left, or both cerebral hemispheres. The reversing group had slower reaction times than the normal group in all conditions. Evidence was insufficient to conclude that mirror-same bilateral presentation facilitated responses of either group over aligned-same or peripheral conditions. This result would have been necessary to indicate the presence of a mirror-reversed code across the hemispheres. Research utilizing delayed as well as simultaneous presentation of stimuli to children of various ages would clarify this ambiguity. Bilateral processing across conditions proved easier for both groups, indicating adequate hemispheric integration on a visual-perceptual task even in children who tended to confuse mirror images.

Cognitive deficiencies in emotionally disturbed children.

This research investigated development of cognitive abilities in a normal vs. emotionally disturbed school age population (N = 240) ages 6-12. The Ss had to display skills on the Southern Illinois University Test necessary to show understanding of Piagetian concepts of class inclusion, class exclusion, and complement of set. A three way analysis of variance indicated significant main effects for age, sex, and emotionality factors. There were, however, no significant interactions among these factors. Emotionally disturbed children were not only deficient in the measured cognitive skills, but even the rate of development of these cognitive skills was inferior to that of the normal population.