GENE CONVERSION DURING VECTOR INSERTION IN EMBRYONIC STEM-CELLS

Recombination of an insertion vector into its chromosomal homologue is a conservative event in that both the chromosomal and the vector sequ ences are preserved. However, gene conversion may accompany homologous recombination of an insertion vector, To examine gene conversion in m ore detail we have determined the targeting frequencies and the struct ure of the recombinant alleles generated with a series of vectors whic h target the hprt gene in embryonic stem cells, We demonstrate that ge ne conversion of the introduced mutation does not significantly limit homologous recombination and that gene conversion occurs without a seq uence specific bias for five different mutations. The frequency of the loss of a vector mutation and the gain of a chromosomal sequence is i nversely proportional to the distance between the vector mutation and the double-strand break. The loss of a chromosomal sequence and the ga in of a vector mutation occurs at a low frequency.