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Characterization of a versatile in vitro DNA-packaging system based on hybrid lambda/phi 29 proheads.

We have studied the assembly of bacteriophage lambda head proteins on the phage phi 29 connector to produce in vitro chimeric proheads, whose ability to package different types of DNA depends on the physical integrity of the phi 29 connector. Terminal protein-free phi 29 as well as nonviral DNAs have been shown to be efficiently packaged by this hybrid system. An RNA, that can be provided by any of the extracts used in the complementation mixture, was required for DNA packaging, both by the hybrid system as well as by the homologous lambda system. The DNA-packaging activity of RNase-treated proheads can be restored by adding a mixture of ribosomal RNAs. There is also a requirement for a minimal length of DNA to be stably packaged. The packaging protein p16 of phi 29 can replace the lambda terminase complex in the in vitro packaging system, both with the chimeric as well as genuine lambda proheads.