Fig. 3. The AU-rich sequence 5′ UUUUAAAUUUU mediates promoter-proximal RNA cross-linking to the 40 kDa protein. The tr and le RNA sequences are shown above, and the fourth and fifth hexamers (nucleotides 31–42) are boxed. The various promoter- proximal RNAs examined are shown schematically as for Figure 2, next to the protein gel used to determine their relative abilities to UV cross-link to the host 40 kDa protein. The alternative sequence exchanges (tr 31–41 and tr 35–37) are shown as gray boxes, and their sequences are shown as well in the box above.