MUTATIONAL ANALYSIS OF STEM-LOOPS IN THE RNA PACKAGING SIGNAL OF THE MOLONEY MURINE LEUKEMIA-VIRUS

The retroviral RNA genome is targeted for incorporation into the nasce nt virion particle by the psi region, a specific block of RNA sequence s near the 5' end. A number of deletions and linker insertion mutation s were introduced into the psi region of cloned DNA of the Moloney mur ine leukemia virus, and the mutants were introduced into cells in cult ure and tested for their ability to direct the assembly of virions and the packaging of viral RNA. Only a small portion of the psi region wa s important for packaging, containing the so-called stem-loops C and D . Additional mutants were used to demonstrate that the base pairing of stem D, and the sequence of loop D, were essential for normal packagi ng of the RNA. Two mutants with alterations near the 5' splice donor w ere also replication-defective, probably due to effects on gene expres sion. The results allow a high-resolution definition of the RNA struct ures required during virus replication in culture, (C) 1998 Academic P ress.