Role of exonuclease in the specificity of bacteriophage T7 DNA packaging.
During morphogenesis in vivo, bacteriophage T7 packages and cuts to mature size an end-to-end concatemer of its nonpermuted, terminally repetitious, double-stranded, mature DNA. Efficient production (90-100%) and packaging (20-35%) of concatemers has also been demonstrated in extracts of T7-infected cells (in vitro) (Son, M., Hayes, S. J., and Serwer, P. [1988] Virology 162, 38-46). By use of both this procedure of in vitro DNA packaging and in-gel hybridization to packaged DNA fractionated by agarose gel electrophoresis, the specificity of packaging in vitro is found to depend on the presence of T7 gene 6 exonuclease (p6). In the absence of p6 in vitro, no concatemerization is detected and packaging of DNA nonhomologous to T7 DNA (bacteriophage P22 DNA) is as efficient (0.05-1.1%) as the packaging of monomeric T7 DNA. Addition of p6 in vitro both stimulates the concatemerization-packaging of T7 DNA and suppresses the packaging of P22 DNA. The packaging efficiency for concatemeric T7 DNA is 29-611 x higher than that for monomeric T7 DNA. Inhibition of the packaging of P22 DNA by p6 is correlated with the formation of single-stranded P22 DNA ends. These data are explained by the hypothesis that a DNA molecule with a single-stranded end is packaged less efficiently than the same DNA without the single-stranded end. Testing this hypothesis in vivo reveals that both p6 and gene 3 endonuclease contribute to suppressing the packaging of host DNA.
Son
M
M
Department of Biochemistry, University of Texas, Health Science Center, San Antonio 78284-7760.
Serwer
P
P
D002213:Capsid / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism*; D004586:Electrophoresis; D004926:Escherichia coli / Q000235:genetics; D005092:Exonucleases / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D013604:T-Phages / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
D004279:DNA, Viral; D005092:Exonucleases