Comparative Genetics of the Poly-Q Tract of Ataxin-1 and Its Binding Protein PQBP-1

Human PQBP-1 is known to interact with triplet repeat disease gene products such as ataxin and huntingtin through their poly-glutamine (poly-Q) tracts. The poly-Q tracts show extensive variation in both the number and the configuration of repeats among species. A surface plasmon resonance assay showed clear interaction between human PQBP-1 and Q(11), representative of the poly-Q tract of the ataxin-1 of Old World monkeys. No response was observed using Q(2)PQ(2)P(4)Q(2), representative of the poly-Q tract of the ataxin-1 of New World monkeys. This implies that the interaction of human PQBP-1 with ataxin-1 is limited to humans and closely related species. Comparison of the human and mouse PQBP-1 sequences showed an elevated amino acid substitution rate in the polar amino acid-rich domain of PQBP-1 that is responsible for binding to poly-Q tracts. This could have been advantageous to the new biological function of human PQBP-1 through poly-Q tracts.     

Comparative aspects of polyglutamine binding domain in PQBP-1 among Vertebrata

We investigated the evolutionary conservation of polyglutamine binding protein-1 (PQBP-1) among Vertebrata. PQBP-1s were highly conserved and shared the same domain features including a WW domain, a polar amino acid rich domain (PRD), a nuclear localization signal (NLS), and a C-terminal domain (CTD) among Eutheria, but not always among Vertebrata. PQBP-1s of Vertebrata contained a variable region in the middle portion corresponding to the position of PRD. The full form of PRD including both 7aa and DR/ER repeats was specific to Eutheria. PRD of non-eutherian Amniota was minimal. Amphibia had no PRD. The DR/ER repeat was solo in fishes. Agnatha PRD was also rich in polar amino acids, but contained no repetitive sequence. We investigated 3 polyQ-containing proteins known to interact with PQBP-1: BRN-2, Huntingtin, and ATAXIN-1, and showed a diverse nature of protein-protein interaction in Vertebrata. There appears to be no interaction between PQBP-1 and BRN-2, Huntingtin, or ATAXIN-1 in Amphibia, while the interaction between PQBP-1 and BRN-2 is expected to be conserved among Mammalia, and the interaction between PQBP-1 and Huntingtin or ATAXIN-1 depends on the lineage in Eutheria.     

Structure and evolution of the mitochondrial control region of the pollen beetle Meligethes thalassophilus (Coleoptera: Nitidulidae).

The organization of the mitochondrial DNA (mtDNA) control region (CR) of the pollen beetle Meligethes thalassophilus is described. This mtDNA CR represents the longest sequenced for beetles so far, since the entire nucleotide sequence ranges from approximately 5000 to approximately 5500 bp. The CR of M. thalassophilus is organized in three distinct domains: a conserved domain near the tRNAIle gene, a variable domain flanking the 12S rRNA gene, and a relatively large central tandem array made up of a variable number of approximately 170 bp repeats that is responsible for the intraspecific length variation observed. Like other CRs found in insects, the M. thalassophilus CR contains two long homopolymeric runs that may be involved in mtDNA replication. Furthermore, conserved stem-and-loop structures in the repetitive domain were identified and their possible role in generating length variation is examined. Intraspecific comparison of the tandem repeat elements of M. thalassophilus suggests mechanisms of concerted evolution leading to homogenization of the repetitive region. The utility of such an array of tandem repeats as a genetic marker for assessing population-level variability and evolutionary relationships among populations is discussed. Finally, the technical difficulties found in isolating the mtDNA CR in beetles are remarked upon.     

Polyglutamine tract-binding protein-1 binds to U5-15kD via a continuous 23-residue segment of the C-terminal domain

Polyglutamine tract-binding protein-1 (PQBP-1) is a nuclear protein that interacts with various proteins, including RNA polymerase II and the spliceosomal protein U5-15kD. PQBP-1 is known to be associated with X-linked mental retardation in which a frameshift mutation in the PQBP-1 gene occurs. In the present study, we demonstrate that PQBP-1 binds to U5-15kD via a continuous 23-residue segment within its C-terminal domain. Intriguingly, this segment is lost in the frameshift mutants of PQBP-1 associated with X-linked mental retardation. These findings suggest that the frameshift mutations in the PQBP-1 gene lead to expression of mutants lacking the ability to interact with U5-15kD.