Budding

The term "budding" translates as "budding" and in biology refers to a form of asexual reproduction in which a new individual develops from a generative anatomical point on the parent organism. In some species, budding can occur from almost any point on the body, but in many cases budding is restricted to specialized areas. The initial protrusion of proliferating cytoplasm or cells, the bud, eventually develops into an organism that duplicates the parent.

The new individual may detach to exist independently, or the buds may remain together and form aggregates or colonies.

Budding is characteristic of a few unicellular organisms (e.g., certain bacteria, yeasts, and protozoa). However, a number of metazoans (e.g., certain cnidarian species) regularly reproduce by budding.

In virology, budding in enveloped viruses is the final step of their morphogenesis in the host cell. Budding is simultaneously associated with envelopment of the capsid with a cellular lipid membrane and shedding of a new virion.

The sites of envelopment may vary. Herpesviridae bud at the nuclear membrane in the space between the inner and outer nuclear membranes into the cytoplasmic cisternae and then reach the cell surface in vesicles. Coronoviridae bud at the endoplasmic reticulum membrane (budding at the ER membrane) and are also delivered to the cell membrane in vesicles. Paramyxoviridae envelop their nucleocapsid at the outer cell membrane upon exit from the cell (budding at the cell membrane).

The reaction steps at a membrane vary depending on the virus:

• Curvature of the membrane by interaction of envelope proteins and attachment of a closed capsid.
• Binding of the envelope proteins to capsomers, budding with formation of a capsid and insertion of the nucleic acid.
• Interaction of the coat proteins mediated by matrix proteins and coating of several helical capsids.

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