Genetic remodeling and transcriptional remodeling of subtelomeric heterochromatin are different

The structure, the extension, and the regulatory functions of telomeric and subtelomeric heterochromatin are not completely understood partly due to the difficulty of separating structural from functional features. We have previously observed that genetic alterations of telomeric heterochromatin components relieve transcriptional silencing. We have developed an analytical system allowing the separate determination of the effects of transcription and of genetic alterations on the subtelomeric structures. The uncoupled analysis, performed on the left extremity of chromosome III of Saccharomyces cerevisiae, consists of genetic dissections, induction of transcription of a resident gene, and chromatin analysis. The results allow (i) the determination of the precise localization and of the extension of heterochromatin (here from 0.9 to 2.6 kb from the innermost extremity of the C 1 - 3 A tract) and (ii) the definition of the transcription and of the genetically induced chromatin remodelings and of their marked differences, thus allowing (iii) specific analyses of the structural effects of the genetic modification of the heterochromatin components.