RECONSTITUTION OF INFECTIVE BACTERIOPHAGE QBETA

Infective and noninfective particles were reconstituted in vitro from purified ribonucleicacid, coat protein, and a minor protein of the bacteriophage Qβ. These individual componentscontained no infectious units but the ribonucleic acid was infectious in spheroplasts. Noninfectiveparticles appeared to have similar size, shape, antigenicity, and ultraviolet absorption spectra asauthentic phage, but differed in sedimentation coefficient and ribonuclease resistance. Formation of particles was related to input coat protein to ribonucleic acid ratio. The average sedimentation coefficient of the ribonucleic acid-protein complex increased from 30 to 70 S with increasing ratios of coat protein to ribonucleic acid. Infectivity of reconstituted particles was dependent upon the presence of the minor protein component in the reaction mixture. A linear response of infectivitywas observed with increasing amount of this component with an optimal coat protein to ribonucleic acid ratio. Reconstituted infective particles sedimented as authentic Qβ phage in sucrose gradients, while noninfective particles, deficient in coat protein but containing the minor protein, sedimented lighter than the infective particles. Thus, reconstitution of infective Qβ particle in vitro requires all of the following conditions: (1) biologically active RNA, (2) sufficient coat protein to yield 80S particles, and (3) incorporation of another minor protein into the 80S particles. © 1969, American Chemical Society. All rights reserved.