Identification of a murine homolog of the human adenosine deaminase thymic enhancer

Abstract

We have identified a 236-bp first intron segment of the mouse adenosine deaminase gene ( ADA) that shares 71.1% identity with the human ADA thymic enhancer. This segment has the same natural orientation as the human enhancer and a relative location within the first intron very analogous to that of the human enhancer. Four highly conserved regions were defined within this segment, including a 72-bp region having 83.6% identity with a segment containing the critical human enhancer core. Several consensus binding sequences were also conserved within these regions. Transient transfection assays in human and murine T-cell lines revealed that a 1.8-kb murine genomic fragment harboring the 236-bp segment functions as a weak activator of both the human and mouse ADA promoters. In contrast, a 2.3-kb human enhancer fragment exhibited high-level activation in conjunction with either the human or mouse ADA promoter in both the MOLT 4 (human) and S49 (murine) T-cell lines. Interestingly, the murine ADA promoter is significantly stronger than the human promoter in driving cat expression in transient transfection assays in all the T-cell lines tested.