title: Exclusion of small terminase mediated DNA threading models for genome packaging in bacteriophage T4.
abstract: Tailed bacteriophages and herpes viruses use powerful molecular machines to package their genomes. The packaging machine consists of three components: portal, motor (large terminase; TerL) and regulator (small terminase; TerS). Portal, a dodecamer, and motor, a pentamer, form two concentric rings at the special five-fold vertex of the icosahedral capsid. Powered by ATPase, the motor ratchets DNA into the capsid through the portal channel. TerS is essential for packaging, particularly for genome recognition, but its mechanism is unknown and controversial. Structures of gear-shaped TerS rings inspired models that invoke DNA threading through the central channel. Here, we report that mutations of basic residues that line phage T4 TerS (gp16) channel do not disrupt DNA binding. Even deletion of the entire channel helix retained DNA binding and produced progeny phage in vivo On the other hand, large oligomers of TerS (11-mers/12-mers), but not small oligomers (trimers to hexamers), bind DNA. These results suggest that TerS oligomerization creates a large outer surface, which, but not the interior of the channel, is critical for function, probably to wrap viral genome around the ring during packaging initiation. Hence, models involving TerS-mediated DNA threading may be excluded as an essential mechanism for viral genome packaging.
authors.affiliation: Department of Biology, The Catholic University of America, 620 Michigan Avenue Northeast, Washington, DC 20064, USA Jiangsu Key Laboratory of Marine Pharmaceutical Compound Screening, Huaihai Institute of Technology, Lianyungang 222005, China.
authors.forename: Song
authors.initials: S
authors.lastname: Gao
authors.affiliation: Department of Biology, The Catholic University of America, 620 Michigan Avenue Northeast, Washington, DC 20064, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Biology, The Catholic University of America, 620 Michigan Avenue Northeast, Washington, DC 20064, USA rao@cua.edu.
authors.forename: Venigalla B
authors.initials: VB
authors.lastname: Rao
mesh_terms: D017122:Bacteriophage T4 / Q000502:physiology*; D004279:DNA, Viral / Q000737:chemistry / Q000502:physiology; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000502:physiology*; D004926:Escherichia coli / Q000821:virology; D016679:Genome, Viral; D008958:Models, Molecular; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D017434:Protein Structure, Tertiary; D014764:Viral Proteins / Q000737:chemistry / Q000502:physiology*; D019065:Virus Assembly
chemical_list: D004279:DNA, Viral; D004268:DNA-Binding Proteins; C065037:Gp16 protein, Bacteriophage T4; D014764:Viral Proteins; D004706:Endodeoxyribonucleases; C030894:terminase