RNA-MEDIATED SPECIFICITY OF DNA PACKAGING INTO HYBRID LAMBDA PHI-29 PROHEADS/

A small RNA (pRNA, 174 nt) is known to be essential for DNA packaging in bacteriophage phi29. However, in an in vitro DNA packaging system b ased on hybrid lambda/phi29 proheads (made up of head proteins from ph age lambda and connectors from phage phi29), the specificity of DNA pa ckaging is lost, and different RNA molecules fulfil the requirements f or DNA packaging, albeit with less efficiency than phi29 pRNA. Competi tion assays with RNAs from different sources have shown that phi29 con nectors bind preferentially pRNA. An increase in the efficiency of phi 29 DNA packaging into hybrid proheads induced by phi29 pRNA is observe d because, when phi29 pRNA is incubated with hybrid proheads, phi29 DN A is packaged more efficiently than other DNAs of similar length. Furt hermore, when hybrid proheads carrying phi29 pRNA are incubated with a mixture of DNAs from different sources, phi29 DNA is selectively pack aged, thus indicating that phi29 pRNA determines the specificity of DN A packaging.