Creation of a deletion series of mouse YACs covering a 500 kb region around Xist.

Two mouse YACs, PA-2 and PA-3, contain the Xist gene and are 460 kb and 3.3 Mb long respectively. While PA-2 is non-chimeric, PA-3 contains a substantial proportion of non-contiguous DNA. As a prerequisite to functional studies of the role of this region in X inactivation, we have created a deletion series of YACs that are spaced at approximately 50 kb intervals and were able to eliminate the unwanted chimeric sequences in YAC PA-3. For this purpose, we have constructed mouse B1 fragmentation vectors based on those described for human Alu fragmentation. Having created this series of YAC deletion derivatives, we were able to eliminate efficiently the 10-15% aberrant YACs that arise during the course of a fragmentation experiment by assessing their marker content. The overlap and the opposite orientation of the two YAC inserts permitted the creation of deletions on both sides of the 500 kb region around Xist. The use of this series of YACs in a biological assay will help us define the extent of the sequences necessary to bring about X chromosome inactivation.