Effect of combination gag and 3'U3 modifications on virus titre. (A) Vectors containing both the Δgag and 3'U3 deletions were compared for virus titre using 0.125 ug vector per well. bGHatt19, pHIV1SDm2SEbGHatt19; bGHatt19Δgag, pHIV1SDm2SEbGHatt19Δgag; SVatt19, pHIV1SDm2SESVatt19; SVatt19Δgag, pHIV1SDm2SESVatt19Δgag (pRK1). * = P < 0.001, ANOVA with Holm-Sidak multiple comparison. All results are presented as Mean ± SD (n = 6). (B) Schematic of 5' LTR and gag gene sequence and 3' LTR variants present in the constructs tested. The region of the gag gene deleted in the "Δgag" constructs is indicated by cross hatching. All constructs contain a 19 bp att sequence in the 3' LTR and the R sequence is truncated at the 3' end.