Differential expression of porcine major histocompatibility DNA sequences introduced into mouse L cells.

The expression of a porcine genomic DNA segment containing a major histocompatibility gene and its chromatin structure in mouse L cells have been investigated. The transformed cells, which contain about two copies of the 17.8-kilobase pig DNA insert per haploid genome, stably and uniformly express major histocompatibility antigen on their surfaces. This expression is the result of differential transcription of the 3-kilobase major histocompatibility gene; the other 14 kilobases of pig sequences flanking the coding sequence are not transcribed. Although the entire pig DNA segment is packaged into nucleosomes, only the transcriptionally active DNA sequences are packaged in a DNase I-sensitive conformation. These results suggest that the expression of this foreign DNA is actively regulated in L cells.