The enhancer activity of four DNA fragments previously identified within a 1-Mb region of human chromosome 19 has been investigated. All the fragments have similar tissue-specific profiles: The greatest enhancer activity is observed in HEK293, and the least, in HeLa cells. The enhancers have clear specificity towards the cytomegalovirus promoter in comparison to the SV40 promoter. Functional dissection of one of the fragments (enhancer 14) has shown that only its inner 127-bp part possesses enhancer activity. It is reasonable to suggest that negative regulators, i.e., silencers or insulators, are present in flanking regions of enhancer 14 and limit its effect on the promoter. The activity of enhancer 14 depends on its orientation relative to the promoter, which is uncommon for enhancer elements. The inner 127-bp fragment contains 11 transcription factor binding sites, and 8 of them are factors involved in immune system regulation. Enhancer 14 is located 500 bp upstream of the transcription start site of the TYROBP (DAP12) gene, which codes for a T-killer cell activator protein. It most likely serves as a tissue-specific enhancer for this gene. © 2011 Pleiades Publishing, Ltd.