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The 68C intermolt puff of Drosophila melanogaster contains a cluster of three glue protein genes, Sgs-3, Sgs-7, and Sgs-8. By analysis of chromosomal rearrangements which break near the glue gene cluster, we have established that a region of no more than 20 kb is required for normal expression of the glue genes and for formation of the 68C puff. Using P element-mediated transformation, we have introduced defined segments of the 68C region into the fly genome and assayed the expression of the Sgs-3 gene. Based on the criteria of correct tissue- and stage-specific expression, transcription of an RNA of appropriate size and abundance, and production of an sgs-3 protein, the correctly regulated expression of the Sgs-3 gene requires less than 3.4 kb of total flanking sequences, approximately 2.3 kb 5' and 1.1 kb 3'. Formation of a new intermolt puff at the site of insertion is not observed for all transformants which produce high levels of Sgs-3 RNA. Only transformants in which the introduced DNA from 68C also contains the Sgs-7 and Sgs-8 genes cause a new intermolt puff at the chromosomal location of the insert.

The homeotic mutations in the right half of the bithorax complex of Drosophila cause segmental transformations in the second through the eighth segments of the fly. A chromosomal walk in the bithorax complex has now been extended 215 kb through the right half of the complex, and lesions for over 40 mutations have been located on the DNA map. The mutations can be grouped in a series of phenotypic classes, one for each abdominal segment, although each mutation typically affects more than one segment. The mutant lesions of each class are clustered, and they are aligned on the chromosome in the order of the body segments that they affect. Complementation tests suggest interactions between widely spaced DNA regions; indeed, the right half cannot be split anywhere without some loss of function.

Publisher Summary This chapter discusses steroid-regulated vertebrate genes. The most extensively studied steroid-responsive gene is the mouse mammary tumor virus (MMTV) provirus. In a variety of cell types, chromosomally inserted proviruses give rise to a single transcript, initiating within the left long terminal repeat (LTR). This transcript is present at very low levels until the cells are exposed to a glucocorticoid hormone. Within minutes following hormone treatment, the titre of the MMTV transcript rises, reaching a level that is at least 50-fold above the basal level within 2 hours. Glucocorticoid receptor binding sites are located within the MMTV LTR, and the same region of the LTR is both necessary and sufficient to confer glucocorticoid inducibility. Receptor binding sites are clustered between 80 and 300 base pairs upstream of the transcriptional initiation sites, and additional sites are present at several positions internal to the transcript. The chapter discusses ecdysteroid-responsive genes from drosophila and glue genes.