TABLE 2.

Adenine insertion mutations in the IRES oligo(A) loop

IRES	No. of inserted A residues	Nucleotide at position 769	Total no. of A residues
Wild type		U	5-6/7a
Mutant clones
1	11	A	19
2	13	A	21
3	15	A	23
4	16	A	24
5	16	A	24
6	17	A	25
7	18	A	26
8	19	A	27
9	23	A	31
10	37	A	45

^aNatural IRES sequences contain five to six A residues; the Clontech IRES used for the construction of TBEV-bc contained seven A residues.