The Biology of Nucleus-Forming Jumbo Phages

Nucleus-forming jumbo bacteriophages display a surprisingly intricate replication cycle inside of bacterial host cells, challenging the long-standing paradigm of prokaryotic simplicity. The phage nucleus encloses phage DNA in a protein shell, strictly uncouples transcription from translation, and facilitates selective protein import and messenger RNA (mRNA) export, serving the same major functions as the eukaryotic nucleus. Infection of host cells by these phages begins with the formation of a transcriptionally active membrane-bound early phage infection vesicle, demonstrating that these phages are capable of constructing subcellular compartments composed of lipids and proteins. Here, we review the current body of literature revealing the complexities of nucleus-forming phages and the history of the major discoveries. Studies of these phages are revealing new insights into basic principles of subcellular organization, viral speciation, and intracellular viral competition.