A unicellular form of fungi. Some fungi (for example Saccharomyces cerevisiae) are only known to reproduce as yeast while other fungi (for example, Candida albicans) are dimorphic, reproducing as yeast under certain conditions and as filamentous mycelia under other growth conditions. Because it is so widely used in studies of Eukaryotic genetics, the term yeast often refers to S. cerevisiae when a specific genus is not indicated.

Yeast artificial chromosome (YAC)
A cloning vector which contains sequences from a yeast chromosome required for DNA replication and segregration. Often used for cloning very large fragments of DNA.

Yeast episomal plasmid (YEp)
A yeast vector carrying the 2 Ám circle origin of replication.

Yeast extract
A water soluble preparation extracted from common yeast. Yeast extract is rich in amino acids, peptides, B vitamins, and trace elements. Commonly used in rich media.

Yeast integrative plasmid (YIp)
A yeast vector that relies on integration into the host chromosome for replication.

Yeast replicative plasmid (YRp)
A yeast vector that carries a chromosomal origin of replication.

Yeast two-hybrid system
An approach developed by Stan Fields and colleagues in 1989 to identify protein-protein interactions in vivo. Proteins (aka "prey") that interact with other, known proteins (aka "bait") are identified by using a reporter system that relies upon interaction between the two proteins. A variety of versions of this system are available, but the basic format involves the construction of two distinct hybrid proteins fused to different reporter genes: in the first the "bait" protein is fused to a transcription factor, and in the second the "prey" protein is fused to a related transcription factor. If the bait and prey proteins interact the two reporter genes fused to the proteins are brought into proximity with each other, producing a specific signal.