Cohesive Ends

Abstract

Cohesive ends are short, complementary single-stranded (ss) extensions of the strands of linear double-stranded (ds) DNA molecules. Annealing of the cohesive ends enables the DNA molecules which possess them to form monomeric or multimeric circles, or linear multimers. 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 are from 7 to 21 nucleotides long, and they can be at either the 5′- or 3′-end of the DNA strand. When a cohesive end virus infects a host cell, the linear DNA molecule circularizes via cohesive end annealing. Circle formation protects the virus chromosome ends from attack by host cell nucleases that attack dsDNA ends. During DNA replication by cohesive end phages, the circular DNA molecule replicates to produce monomeric progeny rings. Late in 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.