VP5 destabilizes RNA helices in a bidirectional manner. Purified MBP-VP5 was incubated with (A) 3′-tailed RNA helix (RNA1/RNA4), (B) 5′-tailed RNA helix (RNA1/RNA5) or (C) blunt-ended RNA helix (RNA1/RNA2) as illustrated in the left panels. Asterisk indicates the HEX-labeled strand (RNA1). The preparations of these destabilizing substrates are indicated in ‘Materials and Methods’ section. RNA helix substrate (0.1 pmol) was incubated in standard reaction mixtures in the presence or absence of 10 pmol MBP-VP5 as indicated, and the destabilizing activity was determined via gel electrophoresis and scanning on a Typhoon 9200. Lane 1, boiled reaction mixture without protein supplementation; lane 2, reaction mixture without protein supplementation; lane 3, reaction mixture with MBP alone; and lane 4, reaction mixture with MBP-VP5.