The gamma 1 heavy chain gene includes all of the cis-acting elements necessary for expression of properly regulated germ-line transcripts.

The regulation of heavy chain switch recombination and the production of germ-line transcripts are highly correlated. IL-4 induces the production of murine gamma 1 germ-line transcripts, and much, if not all, of the regulation is transcriptional. We have investigated the cis-acting elements involved in the regulation of expression of germ-line transcripts by preparing transgenes with the gamma 1 locus. A construct that includes 5' flanking regions, I gamma 1, S gamma 1, and C gamma 1, is regulated like the endogenous gene. Deletion of either most of S gamma 1 or most of C gamma 1 does not alter the correctly regulated expression of the transgenes. An element common to these three different gamma 1 transgenes confers insertion-site independence and copy-number dependence on the transgenes. Finally, the absolute amount of gamma 1-line transcripts is regulated, as transgenic mice with more than 30 gamma 1 genes express no more germ-line transcripts than nontransgenic mice.