Expanding the Diversity of Mycobacteriophages: Insights into Genome Architecture and Evolution
Figure 7
Immunity theft in mycobacteriophage LRRHood?
A. LRRHood is a Cluster C1 phage that contains a ∼1.4 kbp insertion relative to other C1 phages such as Cali. The insertion contains gene 44 encoding a repressor with >99% identity to Subcluster A1 repressors such as Bxb1 gp69. LRRHood does not contain any copies of the repressor binding site, and we propose that its gene 44 functions to protect LRRHood-infected cells from superinfection by Subcluster A1 phages. B. LRRHood gene 44 is one of four genes (43–46) that are absent from the related phage Cali. The 1.35 kbp additional DNA in LRRHood is flanked by 29 bp direct repeats, of which there is only a single copy in Cali and other Cluster C1 phages. Presumably, either LRRHood acquired this 1.35 kbp segment from another phage by recombination within the 29 bp region, or it has been lost from each of the other Cluster C1 phages. The 29 bp repeat is shown in the red box and is present once in Cali at the extreme 3′ end of gene 46, and twice in LRRHood in the end of gene 42 and upstream of gene 47. The upstream and downstream regions common to LRRHood and Cali are shown in green and blue respectively.