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 produ ction of murine gamma 1 germ-line transcripts, and much, if not all, o f the regulation is transcriptional. We have investigated the cis-acti ng elements involved in the regulation of expression of germ-line tran scripts by preparing transgenes with the gamma 1 locus. A construct th at 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 ga mma 1 or most of C gamma 1 does not alter the correctly regulated expr ession of the transgenes. An element common to these three different g amma 1 transgenes confers insertion-site independence and copy-number dependence on the transgenes. Finally, the absolute amount of gamma 1 germ-line transcripts is regulated, as transgenic mice with more than 30 gamma 1 genes express no more germ-line transcripts than nontransge nic mice.