LCR-dependent gene expression in beta-globin YAC transgenics: detailed structural studies validate functional analysis even in the presence of fragmented YACs

Yeast artificial chromosome (YAC) transgenesis is associated with a high fr equency of deletions in the integrated transgenes. To determine the impact of these rearrangements on the ability to derive structure-function relatio nships using YACs, transgenic mice were generated with 248 or 155 kb beta-g lobin locus YACs. The transgenics were examined for structural integrity of the YAC using an approach of structural analysis that unambiguously demons trates intactness of YAC transgene copies. Globin gene expression pier copy of each integrated transgene and the profiles of globin gene expression du ring development were determined. Diverse deletion patterns were observed i n one or more integrated YACs in all the 248 and most of the 155 kb transge nic lines we analyzed. However, when the structure of the major regulatory element of the beta-globin locus, the locus control region, was preserved, the genes of the beta-globin locus functioned normally and globin transgene s of both the 248 and 155 kb beta-YACs were expressed in a position-indepen dent, copy number-dependent manner. Furthermore, the globin genes of both b eta-YACs displayed normal developmental regulation. We conclude that YACs c an be used for analysis of structure-function relationships of large genes or multigene loci in spite of the tendency for rearrangements and deletions of the integrated transgenes. However, detailed structural evidence for in tegrity and continuity of locus sequences is required for correct interpret ation of functional data.