BACTERIOPHAGES OF STREPTOCOCCUS-PNEUMONIAE - A MOLECULAR APPROACH

We have characterized four families of pneumococcal phages with remark able morphological and physiological differences. Dp-1 and Cp-1 are ly tic phages, whereas HB-3 and EJ-1 are temperate phages. Interestingly, Cp-1 and HB-3 have a terminal protein covalently linked to the 5' end s of their lineal DNAs. In the case of Dp-1, we have found that the ch oline residues of the teichoic acid were essential components of the p hage receptors. We have also developed a transfection system using mat ure DNAs from Dp-4 and Cp-1. In the latter case, the transfecting acti vity of the DNA was destroyed by treatment with proteolytic enzymes, a feature also shared by the genomes of several small Bacillus phages. DNA replication was investigated in the case of Dp-4 and Cp-1 phages. The terminal protein linked to Cp-1 DNA plays a key role in the peculi ar mechanism of DNA replication that has been coined as protein-primin g. Recently, the linear 19,345-bp double-stranded DNA of Cp-1 has been completely sequenced, several of its gene products have been analyzed , and a complete transcriptional map has been ellaborated. Most of the pneumococcal lysins exhibit an absolute dependence of the presence of choline in the cell wall substrate for activity, and phage lysis requ ires, as reported for other systems, the action of a second phage-enco ded protein, the holin, which presumably forms some kind of lesion in the membrane. The two lytic gene cassettes, from EJ-1 and Cp-1 phages, have been cloned and expressed in heterologous and homologous systems . The finding that some lysogenic strains of Streptococcus pneumoniae harbor phage remnants has provided important clues on the interchanges between phage and bacteria and supports the view of the chimeric orig in of phages.