Studies on a Possible Precursor in the Self Assembly of the Bacteriophage fr.

Abstract

Complex I , a complex consisting of I RNA strand and 6 protein subunits of the icosahedral RNA-phage fr was formed. The protein subunits bind on more than one site to the RNA. Complex I is very specific in respect to the RNA partner and its formation renders the RNA neither more nor less advantageous in forming phage-like particles with additional protein.The icosahedral capsid of the RNA bacteriophage fr and of related phages can be reconstituted in vitro [l-41. Different types of RNA have catalytic function for the capsid formation and are packed into the capsid. A low amount of infectivity can be restored if fr RNA or the RNA of related phages is used, however, the bulk of particles remains non-infectious, fails to adsorb to the bacterial host and exposes part of its RNA to ribonuclease digestion, properties similar to those of defective particles obtained from phages mutant in the maturation factor [5-71.I n the case of the related phages MS2, R17 and f2 it was shown that with amounts of phage RNA increasing the I : 180 ratio, another complex is formed consisting of 5-6 protein subunits per RNA strand [2, Complex I could have further functions : it could act as a precursor for phage and phage-like particles [8] as it was reported for the filamentous DNAbacteriophage fd [16]. I n this case the binding of a few fd-protein subunits, with or without a minor component, to fd DNA seems to be an inescapable condition for phage self assembly.I n contrast, complex1 could be a type of RNA not to be used in bacteriophage formation, in order to preserve its modulated messenger function.Results described in this paper show that complex I can be incorporated into phage-like particles, although it is not a necessary precursor. Compared with RNA, complex1 shows neither an advantage nor a disadvantage in being incorporated into the phage capsid.During an attempt to further characterize complex I , results were obtained strongly indicating that coat protein is bound t o RNA a t more than one site. Isolation of RNA and RNA Fragments Phage RNA was isolated by a %fold phenol extraction for 10 min a t 4'. As an alternative method phage was kept for 5 min a t 37' in 1 O l 0 sodium dodecyl sulfate with subsequent centrifugation in a sucrose gradient and collecting of the material sedimenting a t 28 S [ZO]. To obtain RNA fragments, 1 mg RNA dissolved in 500 pl H,O was treated for 5 min at 37" with 400 pg ribonuclease. Sucrose gradient centrifugation was performed for 2 hours a t 4" and 50,000 rev./ min in the SW50 rotor in a Spinco L2 centrifuge. RNA fragments sedimenting in distinct peaks a t 18S, 11 S, and 6 S were collected. MATERIALS AND METHODS IsolationAll preparations of RNA and RNA fragments were purified by ethanol precipitation.MS2-RNA was a kind gift of T. Sugiyama, tobacco mosaic virus RNA and turnip yellow mosaic virus RNA from K. W. Mundry and L. Bockstahler. ~51.Isolation of fr Protein 500pg fr, optionally labelled with 35S was dissolved in loop1 H,O and added to 2 0 0 4 ice cold glacial acetic acid. After 20 min the...

R 17 Coat Protein Interaction with Multi‐Stranded R 17 RNA

“…The experiments presented show that the interaction of phage coat protein with multi-stranded RNA is similar to that observed with single-stranded RNA [16,18,19]. At high input multiplicities of coat protein, complexes are assembled which contain pha.ge-like particles (assembly complexes).…”

Hexamer of bacteriophage f2 coat protein as a repressor of bacteriophage RNA polymerase synthesis

“…Also, the problem of coat protein distribution along the phage RNA strand in complex I is still open to discussion. It was suggested by Hohn (8) that the six molecules of coat protein present in complex I are bound at several sites on the RNA strand, whereas Ward et al. (16) assumed that the coat protein molecules in complex I are attached at a single site of the RNA molecule.…”