9.B.80 The Bacillus Phage φ29 (a Podovirus) DNA Ejection System (φ29-E) Family
DNA ejection from the phage capsid into the host bacterial cytoplasm is not a passive process. In most cases, both phage and host proteins seem to be involved in pulling at least part of the viral DNA inside the cell. The DNA ejection mechanism of Bacillus subtilis bacteriophage φ29 is a two-step process where the linear DNA penetrates the cell with a right-left polarity. In the first step, approximately 65% of the DNA is pushed into the cell. In the second step, the remaining DNA is actively pulled into the cytoplasm. This step requires protein p17, which is encoded by the right-side early operon that is ejected during the first push step. The membrane protein p16.7, also encoded by the right-side early operon, plays a role in membrane-associated phage DNA replication, and p16.7 is required for efficient execution of the second pull step of DNA ejection (Alcorlo et al., 2007). p16.7 is known as the replication organizer protein. Its 3-D structure with double stranded DNA is known (2BNKA) (Albert et al., 2005; Asensio et al., 2005).
The reaction believed to be catalyzed by the φ29-E system is:
φ29 DNA (capsid) φ29 DNA (host cytoplasm)