Cohesive Ends

Abstract

Cohesive ends are short, complementary single-stranded (ss) extensions of linear double-stranded (ds) DNA molecules. Cohesive ends are found on the genomic DNA molecules of many, but not all, tailed phages. Tailed phages are dsDNA viruses that infect microorganisms. Depending on the specific virus, cohesive ends vary in length from about 8–20 nucleotides, and they can be at either the 5′- or 3′-end of a DNA strand. When a virus that uses cohesive ends infects a host cell, the linear DNA molecule circularizes via cohesive end annealing. Circle formation protects the virus DNA ends from attack by host cell nucleases. During DNA replication by cohesive end phages, the circular DNA molecule at first replicates to produce monomeric progeny rings. Later during the infection, rolling circle replication produces end-to-end multimers of viral DNA molecules. During virus particle assembly, the cohesive ends of virus genomes are regenerated by introduction of staggered nicks. A viral enzyme involved in DNA packaging, called a terminase, carries out the strand nicking that creates the cohesive ends. Terminase also contains an ATP-powered motor domain that translocates the DNA into the viral protein shell. Terminase binds a recognition site on a concatemer, nicks the DNA and separates the cohesive ends. The DNA is then translocated into the shell. When the next, downstream recognition site is encountered by the packaging complex, nicks are introduced, completing the packaging of the viral DNA into the protein shell. https://doi.org/10.1016/B978-0-12-374984-0.00284-9.