EXTRACHROMOSOMAL ELEMENTS SATELLITES

These intracellular suh-viral elements are present as nucleic acid fragments, either as single-stranded DNA or as single- or double-stranded RNA. As satellites do not contain sufficient nucleic acid to code for the proteins necessary to replicate, they rely upon another helper virus to carry out this function. If the second virus does not exist, the satelhte is trapped within the host cell. 

In yeast, satellite nucleic acid is relatively miniscule (Pupko and Graur, 1999) so these fragments are referred to as microsatelhtes. These exist as simple sequence tandem repeats of chromosome-associated DNA, ranging in size from 2 to 5 nucleotides (Young et al., 2000). Because these are chromosome-associated, replication is tied to the host. 

Since the nucleic acid sequence is distinct from that of the host chromosome, microsatellites may serve as genetic markers and, thus, identification tools (Tautz, 1989). Baleiras-Couto et al. (1996) used PCR-enhanced microsatellite nucleic acid to identify Zygosaccharomyces bailii and Z. bisporous involved in a case of food spoilage. Gonzalez-Techera et al. (2001) and Perez et al. (2001) also reported differentiation and identification of wine yeasts polymorphic loci containing microsatellite markers. 

Microsatellite loci exhibit significant variability and stability, resulting from a high rate of mutation, which may have important consequences in evolution (Sia et al., 1997 Young et al., 2000). Further, not all tandem repeats are polymorphic. As such, care must be taken in using these markers as the basis of relatedness. 

As with other molecular methods, separation and identification of satellite protein requires a suitably equipped and staffed molecular biology laboratory. However, methods may eventually be reduced to kit form, where most labs will have the capability for rapid identification of wine microorganisms using their satellite information. 

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