* Phage viruses are bacteriophages: They infect bacteria, and bacteria lack a nucleus. Their DNA is located in a region called the nucleoid, which is not membrane-bound.
* Phage assembly occurs in the cytoplasm: Phage viruses replicate and assemble their components (capsid proteins, DNA, etc.) in the cytoplasm of the host bacterium. They then use the bacterial cell membrane to bud out or lyse the cell to release new phage particles.
* Nuclear assembly is common in animal viruses: Many animal viruses, such as HIV, herpesviruses, and influenza viruses, use the host cell's nucleus for part of their replication cycle. The nucleus provides a protected environment for viral DNA replication and the production of viral proteins.
In summary: Phage viruses don't assemble in the nucleus because they infect bacteria, which lack a nucleus. They instead assemble in the bacterial cytoplasm.
