Fig. 4: Three gp61 primase binding poses on the gp41 helicase.
From: Structural basis of the T4 bacteriophage primosome assembly and primer synthesis
The three gp61 primase binding poses are observed in the T4 primosome in the presence of ssDNA and ATPγS. The upper panels are sketches of the three EM maps shown in the lower panels. One gp61 primase has two binding sites on the helicase hexamer: the gp61 ZBD binds to two NTDs of one gp41 dimer, and the gp61 RPD binds to two NTDs of a second gp41 dimer. The two NTDs of the third gp41 dimer are unoccupied. In each binding pose, the ssDNA 5′-end emerging from the gp41 helicase consistently passes between the gp61 ZBD and RPD domains. The particle population of each pose is given in parentheses. These poses are similar, but not identical, and are referred to as binding poses 1 through 3. The poses are non-equivalent because of the asymmetric helicase structure due to the presence of a seam between subunits A and F.
