The first intron of the alpha 1(I) collagen gene contains several transcriptional regulatory elements

The first intron of the human alpha 1(I) collagen gene contains a negatively acting element that inhibits transcription of the chloramphenicol acetyltransferase gene driven by either a collagen or an SV40 basal promoter (Bornstein, P., McKay, J., Morishima, J., Devarayalu, S., and Gelinas, R. E. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, in press). We now find that this element is flanked by sequences that both neutralize the inhibitory effect and impart a net positive effect on transcription. A collagen-human growth hormone minigene was constructed in which varying lengths of the collagen intron were retained. Plasmids were transfected into chick tendon fibroblasts, and transcriptional activity was measured by solution hybridization with an antisense RNA probe. The presence of the intact intronic sequence stimulated transcription by a factor of 2-3-fold in comparison with intron-deleted plasmids. However, the isolated negatively acting element inhibited transcription by a factor of 15-20-fold. Surprisingly, this effect was markedly orientation-dependent. Intronic segments flanking the negatively acting element stimulated transcription both when cloned 5' to the collagen promoter in chloramphenicol acetyltransferase-based plasmids and 3' in collagen-human growth hormone constructions. We conclude that expression of the alpha 1(I) collagen gene is controlled by several intronic elements that function coordinately with 5'-flanking and promoter elements.