The 5′ regions of the mouse, rat and human functional p53 genes were isolated and analysed. All three genes possess a non‐coding exon, comprising exclusively 5′ untranslated sequences. This exon contains extensive diad symmetry near the 5′ end of p53 mRNA, possibly allowing for the formation of a stable hairpin structure in this mRNA. The nucleotide sequence within this hairpin element is highly conserved among the species. A DNA stretch of 225 bp preceding the p53 mRNA cap site possesses distinct promoter activity when assayed in the CAT system. However, this activity is practically abolished when further upstream p53 sequences (approximately 120 bp) are included in front of the CAT gene. This suggests that the control of p53 gene expression is complex and involves a negative regulatory element.

A 2.5‐kb cDNA clone for human p53 tumor antigen has been isolated. This clone contains the entire coding region including 135 bp upstream of the first ATG. Comparison of the nucleotide sequence of human p53 and mouse p53 demonstrates that the first ATG in human p53 corresponds to the second ATG (codon No. 4) in mouse p53. The human p53 comprises 393 residues and is longer than the mouse p53 due to six additional codons present at the region corresponding to exon 4 of the mouse p53 gene. The DNA sequence homology between the coding regions of mouse and human p53 is 81% and the conservation of homology is not equally distributed along the molecule. When inserted into SV40‐based expression vectors the human p53 cDNA successfully directs the production of a polypeptide with an apparent mol. wt. of 55 kd which can be precipitated by monoclonal antibodies to p53.

DNA puffs occur in Sciarid salivary gland chromosomes; they are sites of DNA amplification and intense transcription and they appear to encode secreted structural proteins needed for pupation. In this report we have used P-element transformation of Drosophila to study regulation of a Sciara DNA puff gene. We found that a 718-bp promoter fragment of DNA puff gene II/9-1 from Sciara coprophila directs expression of the bacterial reporter gene CAT in late prepupal salivary glands of transgenic Drosophila melanogaster. The identical tissue and analogous stage specificity indicate that some aspects of the ecdysone response are evolutionarily conserved between Drosophila and Sciara. When transgenic salivary glands are cultured in vitro, CAT activity is rapidly induced by ecdysone, suggesting direct control of gene expression by the ecdysone receptor. Putative stage-specific factors limit expression of the chimeric Sciara-CAT gene in transgenic Drosophila to late prepupae but not to third instar larvae when ecdysone titers are also high.

In vivo transformation studies have been performed using fusion constructs of chorion DNA and the alcohol dehydrogenase (Adh) structural gene. The results indicate that almost exclusively 5′ flanking DNA regions of the early (s36) and late (s15) chorion genes suffice for conferring normal chorion developmental specificity (sex, tissue and temporal) on the reporter gene. In the case of s15, the proximal 5′ flanking DNA up to position −370 is sufficient for specificity. However, quantitative analysis indicates that one or more elements within or downstream of the s15 gene are required, either transcriptionally or post‐transcriptionally, for attainment of an mRNA level comparable to that of the endogenous s15 gene (corrected for amplification); in the absence of such element(s), the average level of Adh transcript produced by fusion gene constructs is 18‐fold lower.