An Ectopic Copy of the Drosophila Ftz Associated SAR Neither Reorganizes Local Chromatin Structure nor Hinders Elution of a Chromatin Fragment from Isolated Nuclei

In vitro assays using detergent extracted nuclei allow the operational definition of SARs--specific sequences in the chromosome which are thought to interact with a structural matrix or scaffold. This interaction results in the formation of large stable protein-DNA complexes. We have used P-element transformation to introduce a characterized SAR into the Drosophila genome. The standard assay, which uses detergent extracted nuclei, shows that the ectopic SAR is indeed bound to the scaffold. However, in unextracted nuclei, a chromatin fragment containing the SAR sequence is eluted from the nucleus as readily as a fragment which lacks an SAR. Furthermore, an analysis of the accessibility of the neighbouring chromosomal restriction sites in unextracted nuclei indicates that the introduction of this ectopic SAR does not influence the local structure of chromatin. We conclude that the ectopic SAR site is not attached to a nuclear scaffold or matrix in vivo.