Figure 4.

Negative elongation factors are required for enhancer-blocking activity of putative insulators like Fab7 and Fab8. Enhancer-blocking lines containing Fab7 (A–J) and Fab8 (K–T) insulators, cloned between divergently placed IAB5/lacZ and 2XPE/white reporters, were tested in elongation factor mutant backgrounds. The Fab7 (A,B) and Fab8 (K,L) line shows lacZ staining in IAB5 pattern (A,K) and white in twist (2XPE) pattern (arrow) (B,L), respectively. In Nelf-E/+ (C,M), Nelf-A/+ (E,O), Spt4/+ (G,Q), and Spt5/+ (I,S) backgrounds the lacZ in situ now displays both the IAB5 as well as the 2XPE patterns for both Fab7 and Fab8 lines, respectively. A similar dual IAB5 and 2XPE pattern was observed for the white in situ in Nelf-E/+ (D,N), Nelf-A/+ (F,P), Spt4/+ (H,R), and Spt5/+ (J,T) backgrounds for Fab7 and Fab8 lines, respectively. The embryos are aligned anterior to the left, posterior to the right, dorsal up, and ventral down.