Transcriptional control of the mouse alpha 2(I) collagen gene: functional deletion analysis of the promoter and evidence for cell-specific expression

A chimeric gene was constructed in which sequences between 2,000 base pairs upstream of the start of transcription of the mouse alpha 2(I) collagen gene and 54 base pairs downstream of this site were fused to the chloramphenicol acetyltransferase (CAT) gene. We present evidence suggesting that this collagen gene segment is sufficient for cell-specific expression of the chimeric gene. Indeed, the levels of CAT activity in transient expression experiments were at least 10 times higher after transfection of NIH 3T3 cells than after transfection of a mouse myeloma cell line, whereas much less difference was found after transfection of these two cell types with pSV2-CAT, a plasmid in which the early simian virus 40 promoter is fused to the CAT gene. Several deletions were introduced in the same 5'-flanking segment of the alpha 2(I) collagen gene, and the effects of these deletions were examined after DNA transfection of the chimeric collagen-CAT gene into NIH 3T3 cells. At least two segments broadly located between -979 and -502 and between -346 and -104 are needed for optimal expression of the chimeric gene. These results were obtained both in transient expression experiments and by analysis of pools of NIH 3T3 cells that were stably transfected with the different mutants. In general, the effects of the deletions on the activity of the alpha 2(I) collagen promoter were analogous, whether the plasmids harbored the simian virus 40 enhancer sequence or not, although the overall levels of expression of the chimeric gene were increased when the recombinant plasmids contained this sequence.