Gene structure of chick lumican and identification of the first exon

Three overlapping genomic clones to chick lumican were isolated and then characterized using restriction enzyme analyses, Southern blot analyses with cDNA probes, and by DNA sequencing. The results showed chick lumican gene to consist of 3 exons with a 2.9-kb first intron and a 4.2-kb second intron. Transcription initiation sites, identified by S1 nuclease experiments using genomic fragments containing exon 1 and by primer extension analysis of RNA, indicated the first exon to be 303 b. Two TATA sequences were 31 and 49 bases upstream of the first exon. The first exon contained all 5' untranslated sequence. The second exon was 896 b and contains 20 b of untranslated sequence, and codes for the start methionine to the end of the 10th leucine rich repeat. The third exon is 880 b and codes for the remainder of the core protein, and 724 b of untranslated 3' sequence. A 1-kb genomic fragment containing a portion of exon 1 and upstream sequence in a luciferase reporter sector showed specific promotor activity in the forward, but not the reverse direction when transfected into corneal fibroblasts. These results show the chick lumican gene to consist of three exons, and that regulatory elements are present within 1 kb upstream of the first exon.