Fig. 1: Lateral transduction of chromosomal DNA.

LT is initiated during the early stages of prophage activation with the prophage remaining integrated in the bacterial chromosome. The mechanism commences with bidirectional in situ replication of the integrated prophage from the phage ori, generating multiple copies of the integrated phage and surrounding bacterial chromosome [1]. Some prophages subsequently excise from the chromosome to generate progeny via the lytic cycle, but in those that remain integrated, the phage small terminase subunit (TerS) recognises the embedded pac site (pink triangle) within the prophage sequence, forming a complex for delivery of the DNA to the large terminase (TerL) subunit [2]. The TerS:DNA complex associates with the large terminase (TerL) subunit, which cleaves and translocates the DNA into available phage capsids until capacity (one headful) is reached, with the initial capsid containing a mixture of phage and chromosomal DNA [3]. When the capsid is filled, the DNA is cleaved once more and the Terminase:DNA complex associates with a new empty capsid to resume the packaging process, generating many processive headfuls containing bacterial chromosomes for subsequent transduction [4].