DNA sequences in the first intron of the human pro-alpha 1(I) collagen gene enhance transcription.

A chimeric gene was constructed in which sequences between 253 base pairs (bp) upstream of the start of transcription of the human pro-alpha 1(I) collagen gene and 117 bp downstream of that site were fused to the human alpha 1-globin gene, at a site immediately upstream of the globin initiation codon. Expression of this and subsequent chimeric gene constructions was investigated in microinjected Xenopus laevis oocytes. Presence of 253 bp of pro-alpha 1(I) collagen gene promoter sequences, containing a CAAT box and a TATA box, resulted in a relatively modest level of expression of the linked globin sequences. Lengthening of the pro-alpha 1(I) collagen gene promoter region to include 2400 bp of upstream sequences, increased transcription of the marker gene to some extent. Strong activation of transcription was obtained when a 782-bp fragment of the first intron of the collagen gene was introduced in chimeric constructions containing only 240 bp of the collagen promoter. An enhancing effect of the intron segment on expression of the marker gene was observed from downstream or upstream positions relative to the initiation site of transcription. Sequencing of the intron segment revealed the presence of four decanucleotide consensus sites for binding of the constitutive transcription factor Sp1, as well as an enhancer "core" motif. Our experiments also showed that the cis-acting region strongly enhance the activity of the pro-alpha 1(I) promoter in transfected fibroblasts. On the basis of these observations we conclude that the segment broadly located between +700 and +1300 in the first intron of the human pro-alpha 1(I) collagen gene contains cis-acting sequences with an enhancer effect on transcription of the gene.