Mammalian development is a complex process involving the coordinated activation and suppression of gene expression. Once differentiated, cells must also maintain the ability to respond to signals that alter the timing and extent of cellspecific transcription. To understand these processes demands an elucidation of the nature of the DNA control sequences associated with regulated genes and the number and nature of trans-acting factors that interact with those sequences. The ability to introduce cloned genes into the germline of mice offers an opportunity to study DNA sequences that control both developmental and tissue-specific gene regulation. We have chosen to investigate the nature of these control sequences in the cloned murine α-foetoprotein (AFP) gene (Krumlauf, Hammer, Tilghman & Brinster, 1985).
The AFP gene forms a small multigene family with the evolutionarily related serum albumin gene (Gorin et al. 1980; Ingram, Scott & Tilghman, 1981).