The compositional structure of Gene Ontology terms.

An analysis of the term names in the Gene Ontology reveals the prevalence of substring relations between terms: 65.3% of all GO terms contain another GO term as a proper substring. This substring relation often coincides with a derivational relationship between the terms. For example, the term regulation of cell proliferation (GO:0042127) is derived from the term cell proliferation (GO:0008283) by addition of the phrase regulation of. Further, we note that particular substrings which are not themselves GO terms (e.g. regulation of in the preceding example) recur frequently and in consistent subtrees of the ontology, and that these frequently occurring substrings often indicate interesting semantic relationships between the related terms. We describe the extent of these phenomena--substring relations between terms, and the recurrence of derivational phrases such as regulation of--and propose that these phenomena can be exploited in various ways to make the information in GO more computationally accessible, to construct a conceptually richer representation of the data encoded in the ontology, and to assist in the analysis of natural language texts.

Effect of dose on the metabolism of 1,1,2,2-tetrabromoethane in F344/N rats after gavage administration.

1,1,2,2-Tetrabromo[U-14C]ethane ([14C]TBE) was used to study the metabolism of TBE in rats. Three graded doses of TBE (1.17, 13.6, and 123 mg/kg; 1 microCi 14C/rat at each dose) were administered by gavage to three groups of four rats each. Excreta samples were collected at various time intervals up to 96 hr. Following euthanization, 14C activity was measured in the excreta, tissues, and carcass. The fraction of the dose exhaled as volatile metabolites of TBE, excluding 14CO2, was approximately 9-10% higher in rats given the high dose of TBE compared to that in rats given either the low or the medium dose. The fraction excreted in the urine decreased with increasing TBE dosage. 1,2-Dibromoethylene and tribromoethylene were identified as exhaled metabolites at the high dose. Three major urinary metabolites were identified: dibromoacetic acid, glyoxylic acid, and oxalic acid. The results of this study indicate that the metabolism of TBE was linear up to a dose of 13.6 mg/kg, but the contribution of various TBE metabolic pathways was different at a dose of 123 mg/kg.