FIG. 3.

Position and structure of the Y(n)X(m)AUG motif within type 1 (enterovirus and rhinovirus) IRES elements. The polypyrimidine tract [Y(n)], spacer [X(m)], and cryptic AUG (asterisks) in the intact HRV2 IRES (A) and in a stem-loop domain VI deletion mutant (B) are indicated. The sequence of X(m) was altered in panel B to put the adjacent cryptic AUG into Kozak context (CUUAUGG to ACCAUGG). (C) Growth characteristics of PVS-RIPO (open squares) and RPδ6 (filled diamonds) in HeLa cells. The IRES deletion construct gave rise to viable virus that grew only slightly less efficiently than did PVS-RIPO in HeLa cells. p.i., postinfection.