Thirty-three nonsense mutants of phage PR4 representing 12 complementation groupswere isolated. One or two mutants of each group were grown on a suppressor-negative (Su-) host and characterized by the following criteria (i) proteins synthesized, (ii) level of phage DNA synthesis, and (iii) ability to assemble particles. We determined the protein and phospholipid compositions of the particles assembled in an Su- host, the presence of DNA in the particles, and the ability of the particles to adsorb to host cells. Finally each complementation group was tested for the ability to lyse an Su- host. We have identified one protein required for DNA synthesis, five proteins required for proper assembly of the protein coat and lipid membrane of the phage, two proteins required for stable insertion of DNA into the virion, a protein required for adsorption, a protein required for attachment of the adsorption protein to the virion, and a phage-encoded lytic enzyme.
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