Characterization of 5' region of the human elastin gene

Muhammad Masud Bashir, University of Pennsylvania


The genomic organization corresponding to the amino terminus of human elastin, a major component of the elastic fibers, has been characterized by constructing and screening a genomic library from human placental DNA. Overlapping genomic clones have been obtained by using a 1.1 kb 5$\sp\prime$ cDNA probe. These clones have been characterized by restriction enzyme analysis and extensive DNA sequencing, and encompasses 38 kilobases of genomic sequences including 11 kilobases 5$\sp\prime$ to the translational initiation codon (ATG). This analysis demonstrated that functionally distinct hydrophobic and cross-linking domains of the protein are segregated into separate exons. The introns greatly vary in their sizes ranging from 83 to 7,100 bases while the exons are relatively short in size with an average of 60 bases. All of the splice junctions and most of the introns have been sequenced. The exon:intron ratio in the 5$\sp\prime$ region of the human elastin gene is 1:27. The 5$\sp\prime$ flanking region lacks a canonical TATA box sequence, is G + C rich and contains several SP1 and AP2 binding sites. Another interesting feature of the 5$\sp\prime$ flanking region is the presence of a Z DNA motif indicated by an extended segment of alternating purines and pyrimidines. Primer extension and S1 nuclease protection experiments indicated that transcription is initiated at multiple sites in the gene. Promoter activity was established with CAT reported gene constructs in transient transfections of rat aortic smooth muscle cells, human lung fibroblasts and HT 1080 human fibrosarcoma cells. The 5$\sp\prime$ deletion constructs of the promoter region revealed several regulatory subregions while the progressive 3$\sp\prime$ $\to$ 5$\sp\prime$ removal of the promoter region resulted in a gradual decrease of promoter activity. The interaction of nuclear factors with the human elastin promoter region was studied with gel mobility shift and competition assays. This analysis indicated that specific complexes are formed between the human elastin promoter and nuclear proteins. Nuclear extracts from elastin producing rat aortic smooth muscle cells and non-elastin producing HeLa cells, produced different types of complexes. This data suggests that the overall regulation of the elastin gene expression is complex and occurs at several levels.

Subject Area

Anatomy & physiology|Biology|Genetics|Molecular biology

Recommended Citation

Bashir, Muhammad Masud, "Characterization of 5' region of the human elastin gene" (1990). Dissertations available from ProQuest. AAI9026518.