Expression of MNV VP2 Is Dependent on ,40-43 nt Upstream of the UAAUG Motif Previous work has suggested that viral termination-reinitiation events show little dependence on sequence information downstream of the ''stop-start'' window but require 45-250 nt of upstream primary sequence [11,14,16.19] . In order to determine the minimal sequence requirements for termination-reinitiation in VP2 expresssion, deletions of increasing size were made from the 59 end of the inserted viral information (Figure 1b) . The stop-start product was synthesised efficiently with up to 43 nt of VP1 information present upstream of the UAAUG motif, and to a lesser extent with 40 nt. However, deletion to 37 nt or less abolished expression of the termination-reinitiation product ( Figure 1b) . These data indicate that only 40 nucleotides of VP1 primary sequence immediately upstream of the stop-start window are required for termination-reinitiation in vitro, although 43 nt are required for full activity.