Abstract
The assembly of double-stranded DNA bacteriophages is dependent on a small terminase protein that normally plays two important roles. Firstly, the small terminase protein specifically recognizes viral DNA and recruits the large terminase protein, which makes the initial cut in the dsDNA. Secondly, once the complex of the small terminase, the large terminase and the DNA has docked to the portal protein, and DNA translocation into a preformed empty procapsid has begun, the small terminase modulates the ATPase activity of the large terminase. Here, the putative small terminase protein from the thermostable bacteriophage G20C, which infects the Gram-negative eubacterium Thermus thermophilus, has been produced, purified and crystallized. Size-exclusion chromatography-multi-angle laser light scattering data indicate that the protein forms oligomers containing nine subunits. Crystals diffracting to 2.8 Å resolution have been obtained. These belonged to space group P2₁2₁2₁, with unit-cell parameters a = 94.31, b = 125.6, c = 162.8 Å. The self-rotation function and Matthews coefficient calculations are consistent with the presence of a nine-subunit oligomer in the asymmetric unit.
Highlights
During the assembly of double-stranded DNA bacteriophages, DNA is usually translocated into preformed procapsids by a molecular motor consisting of the small and large terminase proteins and the portal protein (Casjens, 2011; Feiss & Rao, 2012)
DNA translocation into the procapsid is fuelled by the ATPase activity of the large terminase protein (Sun et al, 2008)
As the small terminase is usually encoded by a gene immediately preceding the large terminase and portal protein genes, and because the corresponding G20C gene had an appropriate size, we decided to clone this gene of G20C
Summary
During the assembly of double-stranded DNA bacteriophages, DNA is usually translocated into preformed procapsids by a molecular motor consisting of the small and large terminase proteins and the portal protein (Casjens, 2011; Feiss & Rao, 2012). The small terminase recognizes the bacteriophage genomic DNA and recruits the large terminase protein. Following DNA cutting by the large terminase, the complex of the two terminase proteins and DNA docks to the portal protein of an empty prophage. DNA translocation into the procapsid is fuelled by the ATPase activity of the large terminase protein (Sun et al, 2008). During DNA translocation, the small terminase protein modulates the ATPase and nuclease activities of the large terminase protein (Gual et al, 2000)
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