Impact of human immunodeficiency virus type 1 RNA dimerization on viral infectivity and of stem-loop B on RNA dimerization and reverse transcription and dissociation of dimerization from packaging

The kissing-loop domain (KLD) encompasses a stem-loop, named kissing-loop o r dimerization initiation site (DIS) hairpin (nucleotides [nt] 248 to 270 i n the human immunodeficiency virus type 1 strains HIV-1(Lai) and HIV-1(Hxb2 )), seated on top of a 12-nt stem-internal loop called stem-loop B (nt 243 to 247 and 271 to 277), Destroying stem-loop B reduced genome dimerization by similar to 50% and proviral DNA synthesis by similar to 85% and left unc hanged the dissociation temperature of dimeric genomic RNA, The most affect ed step of reverse transcription was plus-strand DNA transfer, which was re duced by similar to 80%. Deleting nt 241 to 256 or 200 to 256 did not reduc e genome dimerization significantly more than the destruction of stem-loop B or the DIS hairpin. We conclude that the KLD is nonmodular: mutations in stem-loop B and in the DIS hairpin have similar effects on genome dimerizat ion, reverse transcription, and encapsidation and are also "nonadditive"; i .e., a larger deletion spanning both of these structures has the same effec ts on genome dimerization and encapsidation as if stem-loop B strongly impa cted DIS hairpin function and vice versa, A C258G transversion in the palin drome of the kissing-loop reduced genome dimerization by similar to 50% and viral infectivity by similar to 1.4 log, Two mutations, CGCG261-->UUAA261 (creating a weaker palindrome) and a Delta 241-256 suppressor mutation, wer e each able to reduce genome dimerization but leave genome packaging unaffe cted.