Figure 5.

Stalled Hox promoters may help promote higher-order chromatin organization within the Hox loci. Our results suggest that the stalled promoters contain intrinsic insulator activity that requires NELF (N) and DSIF (D) proteins, and this may help define higher-order loops within gene complexes such as the Hox complex. The stalled Pol II (P) along with the NELF and DSIF complex may interact with putative insulator (In) sequences, as seen for the Abd-B promoter (stalled) and the Fab7 (insulator). Our experiments also suggest that that putative insulator sequences also require NELF and DSIF proteins, and this could be due to sharing of these proteins via the formation of higher-order loops. Such loop domains may help in proper regulation of genes and prevent any aberrant activation from neighboring enhancers (En) (shown by dashed arrow), thus favoring proper gene regulations at the higher-order level.