Purification of DNA-binding proteins of bacteriophage T3 and heir role in in vitro packaging of phage T3 DNA

A 14-kilodalton inner membrane protein of Vibrio cholerae biotype e1 tor confers resistance to group IV choleraphage infection to classical vibrios

Choleraphage phi 149 differentiates the two biotypes, classical and el tor, of Vibrio cholerae. This phage cannot replicate in V. cholerae biotype el tor cells because the concatemeric DNA intermediates produced are unstable and cannot be chased to mature phage DNA. A V. cholerae biotype el tor gene coding for a 14,000-Da inner membrane protein which destabilizes the concatemeric DNA intermediates by hindering their binding to the cell membrane has been identified. Presumably, a 22,000-Da V. cholerae biotype el tor protein might also have a role in conferring phage phi 149 resistance to cells belonging to the biotype el tor. A nucleotide sequence homologous to the 1.2-kb V. cholerae biotype el tor DNA coding for both the 14,000- and 22,000-Da proteins is present in all strains of classical vibrios but is not transcribed. The nucleotide sequence of the gene coding for the 14,000-Da protein has been determined.

Sequence of bacteriophage T3 DNA from gene 2.5 through gene 9

The nucleotide sequence of bacteriophage T3 DNA, from gene 2.5 through gene 9 has been determined. In addition to regulatory sites, the sequence predicts 19 close-packed genes plus two genes that overlap, in a different reading frame, another gene. The majority of these genes are highly homologous to those in the corresponding region of bacteriophage T7. However, there are some genes that are present in one, but not the other, phage. These apparent deletions are almost exactly gene size and thus the close-packed organization of genes remains the same in T3 as in T7. The varying levels of homology between T3 and T7 DNAs, first noted by Davis and Hyman in their study of DNA heteroduplexes, are also demonstrated here by a comparison of T3 and T7 nucleotide sequences. Many regions of extremely high homology immediately abut sequences that have no apparent homology. These data suggest that bacteriophages T3 and T7 have recombined, both with each other and with other members of a pool of T7-like phages, during their co-evolution.

Replication and packaging of choleraphage phi 149 DNA

The intercellular replication of the circularly permuted DNA of choleraphage phi 149 involves a concatemeric DNA structure with a size equivalent to six genome lengths. The synthesis of both monomeric and concatemeric DNAs during replication of phi 149 occurred in the cytoplasm. The concatemers served as the substrate for the synthesis of mature phage DNA, which was eventually packaged by a headful mechanism starting from a unique pac site in the concatemeric DNA. Packaging of DNA into phage heads involved binding of concatemeric DNA to the cell membrane. A scheme involving sequential packaging of five headfuls proceeding in the counterclockwise direction from the pac site is proposed. After infection under high-phosphate conditions, the concatemeric DNA intermediates were not formed, although synthesis of monomeric molecules was unaffected.

A defined in vitro system for packaging of bacteriophage T3 DNA

Using purified components, we have constructed an in vitro system for packaging of mature phage T3 DNA. In addition to mature T3 DNA, the system contained T3 proheads and the products of gene 18 (gp18) and gene 19 (gp19). The reaction required Mg2+, ATP, and polyvinyl alcohol. Spermidine was stimulatory but not absolutely required for the packaging reaction. Polyvinyl alcohol could be replaced by polyethylene glycol. The packaging efficiency decreased with decreasing molecular weight of the polymer, and low molecular weight polyols such as sucrose, sorbitol, and glycerol were inactive. The packaging reaction exhibited a sigmoidal relationship with respect to the concentration of ATP with the concentration for half maximal activity about 15 microM. A nonhydrolyzable ATP analog, adenosine 5'-O-(3-thiotriphosphate), inhibited the packaging reaction.

Isolation and characterization of bacteriophage T3/T7 hybrids and their use in studies on molecular basis of DNA-packaging specificity

In vitro DNA-packaging systems of bacteriophages T3 and T7 packaged homologous DNA more efficiently than heterologous DNA. Packaging of phage DNA proceeds by way of concatemeric intermediates (H. Fujisawa, J. Miyazaki, and T. Minagawa (1978), Virology 87, 394-400). The conversion of mature homologous and heterologous DNAs to concatemers was efficient in both the T3- and T7-packaging systems. In vitro complementation experiments indicate that the gene 19 product (gp19) specifies which DNA enters the capsid. To identify DNA regions recognized by the packaging systems, T3/T7 hybrids were constructed and physical maps of the hybrid DNAs were determined by restriction enzyme analysis. By comparing restriction maps and in vitro packaging of hybrid DNAs, it is concluded that the sequence responsible for specificity of DNA packaging is confined within 5% of the ends of the T3 and T7 genomes.

Purification and properties of gene 18 product of bacteriophage T3

Two noncapsid proteins of T3 and T7 phage, the products of gene 18(gp18) and gp19, are required for DNA packaging. By using in vitro complementation for DNA packaging as an assay system, T3 gp18 was purified to near homogeneity from an extract prepared cells infected with a mutant of gene 19(19- extract). The purified gp18 consisted of a single polypeptide having a molecular weight of 10,000, and was eluted as dimers and higher multimers from Sephadex G-75 columns. T7 gp18 was purified by the same procedures as that for T3 gp18 and behaved in the same manner as T3 gp18 throughout all purification steps. Gp18 from either T3 or T7 phage complemented both T3 and T7 18- extract for DNA packaging. These results indicate that, in contrast to gp19 [H. Fujisawa and M. Yamagishi (1981) Prog. Clin. Biol. Res. 64, 239-252], gp18 does not have specificity for T3 or T7 DNA during the in vitro packaging reaction. T3 gp18 was purified from extract containing functional gp19. The gp18 copurified with the gp19 activity. Gp18 and gp19 activities were stable when they were copurified but were unstable when purified separately. These results suggest that gp18 and gp19 function as a complex in the DNA packaging process. The gp18-gp19 preparation had a prohead-stimulated, DNA-dependent ATPase activity.

On the terminally redundant sequences of bacteriophage T3 DNA

The nucleotide sequences of the termini of mature DNA from T3 phage were determined. A directly repeated sequence of 230 base pairs, corresponding to the terminal redundancy of T3 DNA, was found in the left and right end of the genome. The sequence of the terminal regions of T3 DNA was compared with that of T7 DNA. There are discrete sequences with significant homology, specifically in the regions around the two ends of the terminally redundant sequences. 5'-CCTAAAG and its variants appear frequently in both ends of the genome. T3 DNA fragments carrying the terminally redundant sequences were isolated from concatemeric DNA and analyzed by restriction enzymes.