The dimerization/packaging sequence is dispensable for both the formation of high-molecular-weight RNA complexes within retroviral particles and the synthesis of proviruses of normal structure

Retroviral particles contain a dimer of two genomic RNA molecules, linked by noncovalent intermolecular bonds. Studies by electron microscopy of viral RNA extracted from virions as well as in vitro studies have implicated a sequence, designated the dimer linkage sequence (DLS), in the dimerization process. The DLS has been localized within a short region encompassing the Ψ packaging sequence, between nucleotides 212 and 563 for the Moloney murine leukemia retrovirus (MoMLV) RNA. In this report, we show that vital RNAs lacking both the DLS and Ψ packaging sequences-and even an RNA lacking the first 6,537 nucleotides of MoMLV-can assemble within retroviral particles as high-molecular-weight, slow-migrating, heat-sensitive complexes closely related to those observed for wild-type viral RNAs. Furthermore, we show that proviruses of normal structure are generated upon infection of test cells with retroviral particles which contain the DLS/Ψ-deleted viral RNAs. These observations demonstrate that the DLS and Ψ packaging sequences are not essential in cis to form a functional RNA complex for reverse transcription and integration.