Structure of the bacteriophage phi 29 DNA packaging motor

Motors generating mechanical force, powered by the hydrolysis of ATP, trans locate double-stranded DNA into preformed capsids (proheads) of bacterial v iruses(1,2) and certain animal viruses(3). Here we describe the motor that packages the double-stranded DNA of the Bacillus subtilis bacteriophage phi 29 into a precursor capsid. We determined the structure of the head-tail c onnector-the central component of the phi 29 DNA packaging motor-to 3.2 Ang strom resolution by means of X-ray crystallography. We then fitted the conn ector into the electron densities of the prohead and of the partially packa ged prohead as determined using cryo-electron microscopy and image reconstr uction analysis. Our results suggest that the prohead plus dodecameric conn ector, prohead RNA, viral ATPase and DNA comprise a rotary motor with the h ead-prohead RNA-ATPase complex acting as a stator, the DNA acting as a spin dle, and the connector as a ball-race. The helical nature of the DNA conver ts the rotary action of the connector into translation of the DNA.