The internal head protein Gp16 controls DNA ejection from the bacteriophage T7 virion.
A wild-type T7 virion ejects about 850 bp of the 40 kb genome into the bacterial cell by a transcription-independent process. Internalization of the remainder of the genome normally requires transcription. Inhibition of transcription-independent DNA translocation beyond the leading 850 bp is not absolute but the time taken by a population of phage genomes in overcoming the block averages about 20 minutes at 30 degrees C. There are additional blocks to transcription-independent translocation and less than 20 % of infecting DNA molecules completely penetrate the cell cytoplasm after four hours of infection. Mutant virions containing an altered gene 16 protein either prevent the blocks to transcription-independent DNA translocation or effect rapid release from blocking sites and allow the entire phage DNA molecule to enter the cell at a constant rate of about 75 bp per second. This rate is likely the same at which the leading 850 bp is ejected into the cell from a wild-type virion. All mutations fall into two clusters contained within 380 bp of the 4 kb gene 16, suggesting that a 127 residue segment of gp16 controls DNA ejection from the phage particle. We suggest that this segment of gp16 acts as a clamp to prevent transcription-independent DNA translocation.
Molecular Genetics and Microbiology, and Institute for Cell and Molecular Biology, Austin, TX 78712-1095, USA.
J S
JS
Struthers-Schlinke
W P
WP
Robins
P
P
Kemp
I J
IJ
Molineux
D000595:Amino Acid Sequence; D017123:Bacteriophage T7 / Q000737:chemistry / Q000235:genetics* / Q000254:growth & development / Q000502:physiology*; D015139:Blotting, Southern; D003593:Cytoplasm / Q000821:virology; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology / Q000821:virology; D005814:Genes, Viral / Q000235:genetics; D016679:Genome, Viral; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014758:Viral Core Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015678:Viral Structural Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D004279:DNA, Viral; D014758:Viral Core Proteins; D015678:Viral Structural Proteins; C412714:gene16 product, bacteriophage T7