Figure 23-8: DNA packaging in bacteriophage SPP1. The SPP1 DNA packaging has been divided in five different steps. A, The terminase complex (G1P-G2P, represented as grey ovals and smaller grey circles, respectively) is assembled at one pac site of the phage DNA concatemer and recognizes the portal protein region of the procapsid (representation of the individual components is as in figure 23-5). The arrow indicates the staggered nicks in pacC (see figure 23-7). B, After DNA cutting at pac the encapsidated end (pacR) is translocated into the procapsid and the non-encapsidated end (pacL) is being degraded. C, With translocation of the DNA the scaffolding protein is released and the capsid shell expands. D, When the capsid is filled with DNA the G6P sensor will give the signal for cutting the DNA and transfer the terminase-DNA concatemer complex to another procapsid. E, After the headful cut DNA encapsidation starts again with a new procapsid. The DNA-filled capsid proceeds to the final steps of phage morphogenesis.