title: The P-SSP7 cyanophage has a linear genome with direct terminal repeats.
abstract: P-SSP7 is a T7-like phage that infects the cyanobacterium Prochlorococcus MED4. MED4 is a member of the high-light-adapted Prochlorococcus ecotypes that are abundant in the surface oceans and contribute significantly to primary production. P-SSP7 has become a model system for the investigation of T7-like phages that infect Prochlorococcus. It was classified as T7-like based on genome content and organization. However, because its genome assembled as a circular molecule, it was thought to be circularly permuted and to lack the direct terminal repeats found in other T7-like phages. Here we sequenced the ends of the P-SSP7 genome and found that the genome map is linear and contains a 206 bp repeat at both genome ends. Furthermore, we found that a 728 bp region of the genome originally placed downstream of the last ORF is actually located upstream of the first ORF on the genome map. These findings suggest that P-SSP7 is likely to use the direct terminal repeats for genome replication and packaging in a similar manner to other T7-like phages. Moreover, these results highlight the importance of experimentally verifying the ends of phage genomes, and will facilitate the use of P-SSP7 as a model for the correct assembly and end determination of the many T7-like phages isolated from the marine environment that are currently being sequenced.
authors.affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Gazalah
authors.initials: G
authors.lastname: Sabehi
authors.forename: Debbie
authors.initials: D
authors.lastname: Lindell
mesh_terms: D001435:Bacteriophages / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004279:DNA, Viral / Q000235:genetics / Q000302:isolation & purification; D016679:Genome, Viral; D017902:Podoviridae / Q000235:genetics*; D048929:Prochlorococcus / Q000821:virology*; D020079:Terminal Repeat Sequences
chemical_list: D004279:DNA, Viral