Variable Number Tandem Repeats (VNTR) are short sequences of DNA, nine to one hundred base pairs long, which are repeated in tandem. These sequences are highly recombinogenic, and as such they are very useful to forensic analysis and some have been associated with disease.
A plasmid-based VNTR system which utilizes the yeast Saccharomyces cerevisiae has been developed in order to better understand why these sequences are so recombinogenic. Recombination was initiated by creating a Double Strand Break (DSB) between two homeologous arrays of VNTRs. The plasmid was then transformed into a RAD1 and a $\Delta$rad1 strain of S. cerevisiae in order to understand how the Rad1p affects the ability of VNTRs to repair the DSB.
We observed that when the Rad1p is mutated, it causes a decrease in transformation efficiency and is still able to yield recombinant products. However, no difference in the structure of the product was discernible between the plasmids isolated from the RAD1 and $\Delta$rad1 strains.
Because a major player in recombination, RAD52, is still intact in these cells, it is possible that although Rad1p function does not exist recombination can still occur via a RAD52-dependent mechanism. These studies also show that the amount of homology between the two VNTR arrays is also a major player in the recombination of these sequences.
