Showing papers by "Hiroshi Sakamoto published in 1995"

Four p53 DNA-binding domain peptides bind natural p53-response elements and bend the DNA

Abstract: Recent structural studies of the minimal core DNA-binding domain of p53 (p53DBD) complexed to a single consensus pentamer sequence and of the isolated p53 tetramerization domain have provided valuable insights into their functions, but many questions about their interacting roles and synergism remain unanswered. To better understand these relationships, we have examined the binding of the p53DBD to two biologically important full-response elements (the WAF1 and ribosomal gene cluster sites) by using DNA circularization and analytical ultracentrifugation. We show that the p53DBD binds DNA strongly and cooperatively with p53DBD to DNA binding stoichiometries of 4:1. For the WAF1 element, the mean apparent Kd is (8.3 +/- 1.4) x 10(-8) M, and no intermediate species of lower stoichiometries can be detected. We show further that complex formation induces an axial bend of at least 60 degrees in both response elements. These results, taken collectively, demonstrate that p53DBD possesses the ability to direct the formation of a tight nucleoprotein complex having the same 4:1 DNA-binding stoichiometry as wild-type p53 which is accompanied by a substantial conformational change in the response-element DNA. This suggests that the p53DBD may play a role in the tetramerization function of p53. A possible role in this regard is proposed.

Transcriptional regulation of the Sex-lethal gene by helix-loop-helix proteins

Abstract: Somatic sex determination in Drosophila depends on the expression of Sex-lethal (Sxl), whose level is determined by the relative number of X chromosomes and sets of autosomes (X:A ratio). The first step in regulation of Sxl expression is transcriptional control from its early promoter and several genes encoding transcription factors of the helix-loop-helix (HLH) family such as daughterless (da), sisterless-b (sis-b), deadpan (dpn) and extramacrochaetae (emc) have been implicated. By the use of transfection assays and in vitro binding experiments, here we show that da/sis-b heterodimers bind several sites on the Sxl early promoter with different affinities and consequently tune the level of active transcription from this promoter. Interestingly, our data indicate that repression by the dpn product of da/sis-b dependent activation results from specific binding of dpn protein to a unique site within the promoter. This contrasts with the mode of emc repression, which inhibits the formation of the da/sis-b heterodimers. These results reveal the molecular mechanisms by which Sxl gene transcription is positively or negatively regulated to control somatic sex determination.

Study of π+π− Pair Production in a Two-Photon Process at TRISTAN: VENUS Collaboration

Abstract: We measured the cross section for the γγ→π + π - process in the pion pair invariant mass range of 1.0–1.5 GeV/ c 2 with the VENUS detector at TRISTAN. The γγ decay width of the f 2 (1270) resonance was obtained by using Vermaseren's model and a partial wave analysis. The results from both analyses were in good agreement. The partial wave analysis indicated the presence of a J=0 component around at 1.2 GeV/ c 2 with a resonance-like structure.

Language Learning from Membership Queries and Characteristic Examples

Abstract: This paper introduces the notion of characteristic examples and shows that the notion contributes to language learning in polynomial time. A characteristic example of a language L is an element of L which includes, in a sense, sufficient information to represent L. Every context-free language can be divided into a finite number of languages each of which has a characteristic example and it is decidable whether or not a context-free language has a characteristic example. We present an algorithm that learns parenthesis languages using membership queries and characteristic examples. Our algorithm runs in time polynomial in the number of production rules of a minimal parenthesis grammar and in the length of the longest characteristic example.

Beam tests of the prototype level-1 trigger system and drift tubes with field-shapers proposed for the SDC barrel muon system

Abstract: Mini-tower beam tests were carried out at a test beam line of KEK-PS in order to study the performance of the prototype level-1 trigger system and drift tubes with field-shapers originally designed for the SDC barrel muon detector at the SSC. A mini-tower of 10 layers, 31 drift tubes in total, and a prototype level-1 trigger module were designed and fabricated for the tests. The spatial resolution of about 230 μm was obtained for the tubes. Relatively high rates of multi-pulse signals were observed for most of the tubes. The trigger module designed at KEK using a logic delta- T method was studied for various trigger logics and its performance was found to be very satisfactory.

Language Learning with Characteristic Examples and Membership Queries

Abstract: This paper introduces the notion of characteristic examples for languages and shows that the notion contributes to language learning in polynomial time. A characteristic example of a language L is a string of L which includes, in a sense, sufficient information to represent the language L. We show that any context-free language can be divided into a finite set of languages each of which has a characteristic example. We prove that it is solvable whether or not a context-free language has a characteristic example. Then, we propose a learning model with membership queries and characteristic examples for the class of parenthesis languages. We prove that, for this class, our learning algorithm runs in a polynomial time in the size of a minimal parenthesis grammar which generates the target language and in the length of a longest characteristic example given to the algorithm.

Study of inclusive baryon-antibaryon pair production of p or Λ in two-photon processes

Abstract: Inclusive baryon-antibaryon pair production was studied in two-photon events which were collected at thee + e − collider TRISTAN, and correspond to an integrated luminosity of 303 pb−1. Correlations between a baryon and an antibaryon were studied for their flavors (p orΛ) and their momentum vectors. The experimental results were compared with the expectations from a jet-fragmentation Monte Carlo simulation. We have found that although the ratios of the cross sections of different baryon-flavor combinations are consistent with the Monte Carlo expectations, the cross section shows an excess over the Monte Carlo expectation in a low invariant-mass region of final-state particles at large angles, that indicates a significant contribution from higher-order QCD or non-perturbative effects. The experimental data show no narrow azimuthal-angle correlation, which is expected from a jet-fragmentation Monte Carlo. A search for exclusiveΛ pair production has also been made. We have no candidates and have obtained the upper limit for the cross section.