Characterization of a versatile in vitro DNA-packaging system based on hybrid λ/φ29 proheads

Abstract

We have studied the assembly of bacteriophage λ head proteins on the phage φ29 connector to produce in vitro chimeric proheads, whose ability to package different types of DNA depends on the physical integrity of the φ29 connector. Terminal protein-free φ29 DNA 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 λ 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 pt 6 of φ29 can replace the A terminase complex in the in vitro packaging system, both with the chimeric as well as genuine λ proheads.