Effect of 5'U3 deletions on virus titre. (A) Schematic showing the deletions to the modulatory region of 5'U3 that were analysed. att, integration signal; Sp1, Sp1 binding site; CE, core enhancer. (B) Vector titres using 1 ug vector per well. * = P < 0.05 vs. pRK1, ANOVA on Ranks with Dunns multiple comparison. All results are presented as Mean ± SD (n = 6).