Figure 1. Deletion analysis identifies the minimal attenuator element in SARS-CoV viral sequence.

(A) Schematic drawing of SARS-CoV viral genomic region spanning−1 PRF signal and its upstream element covering sequences 13222–13520 of SARS-CoV. Each of different 5′-viral deletion fragments (annotated by arrow) was cloned into a dual-luciferase−1 PRF reporter with a shortened −1 reading-frame. (B) In vitro −1 PRF assays by SDS-PAGE analysis of ³⁵S methionine-labeled translation products for reporter constructs containing different 5′ deletions of the ATT element (left) and the relative frameshifting activities of different deletion mutants (right). The two major bands in each lane correspond to 0 (lower) and −1 (higher) frame translation products. The relative extent of frameshifting was determined as the ratio between each mutant and the 13390–13520 containing reporter construct (being treated as 100%). The value for each construct is presented as mean±SD (error bars) of triplicate experiments.