Michael Dean

CHAPTER 3 – HUMAN AND DROSOPHILA ABC PROTEINS

The identification of the complete set of 48 human ABC genes has allowed a comprehensive phylogenetic analysis of the superfamily. The nomenclature of ABC transporters is in excellent agreement with the phylogenetic groups obtained. In particular, all major ABC transporter families are represented in the human tree by stable clusters with high bootstrap values. This analysis provides evidence for frequent domain duplication of ATP-binding domains in ABC transporters. In nearly all cases, both ATP-binding domains encoded within a gene are more closely related to each other than to ATP-binding domains from ABC transporter genes of other subfamilies. This is unlikely to represent a concerted evolution of domains within the same gene, as the two domains within each gene are usually substantially diverged. A far more likely scenario suggests several independent duplication events rather than a single ancestral duplication. Analysis of the Drosophila genome sequence identified 56 ABC genes with at least one representative of each of the known mammalian subfamilies.

Response Biases: Tonic Neck Response and Aftercontraction Phenomenon

Abstract In the present experiments, an attempt was made to document possible response biases resulting from changes in head position and to determine if this source of bias is additive or interactive in its influence on learned motor responses when paired with response biases arising from the aftercontraction phenomenon (Shea, Shebilske, Kohl, & Guadagnoli, 1991). The results of Experiments 1 and 2 indicated that the influence of head position on response biases was dependent on head position during acquisition and on the direction in which the head was turned with respect to the flexors and extensors involved in the movement; the magnitude of the effect tended to increase as the force of the contraction increased. In Experiment 3, increases in the intensity of a prior contraction were reflected in the magnitude of the response bias and changes in head position were reflected in corresponding changes in response biases. These findings are consistent with the influence of the aftercontraction phenomenon a...