EVIDENCE THAT A KISSING LOOP STRUCTURE FACILITATES GENOMIC RNA DIMERIZATION IN HIV-1

Genomic RNA isolated from retroviral particles is a dimer composed of two identical strands. A region called the dimer linkage signal close to the 5' end of the RNA may be involved in forming the dimer. Several models for the formation of the HIV-1 RNA dimer have been proposed. I n the kissing loop model, dimerisation results from base-pairing betwe en homologous sequences in an RNA stem-loop. In the guanine tetrad mod el interstrand guanine contacts form the dimer. We have made mutations preventing the dimerisation of subgenomic RNAs in vitro by these mech anisms. To prevent the kissing loop dimer forming we changed the compl ementary loop sequence from 711GCGCGC716 to 711AAACGC716. To prevent t he guanine tetrad dimer forming we changed G819 to U. These mutations were introduced into a clone of HIV-1(NL4-3) separately and collective ly. All three clones produced infectious virions. Dimeric RNA with sim ilar thermal stabilities was isolated from viruses containing either t he single or the double mutations. The results suggest that sequences involved in forming a guanine tetrad are not important for HIV-1 RNA d imerisation. In contrast sequences involved in forming a kissing loop complex are not absolutely required, but are important in forming a st able HIV-1 RNA dimer. (C) 1996 Academic Press Limited.