FUNCTIONAL DISSECTION OF THE MURINE LCK DISTAL PROMOTER

The lymphocyte-specific proto-oncogene Ick is transcribed from two dev elopmentally regulated, independently functioning promoters. The proxi mal promoter is used in thymocytes, but not in peripheral T lymphocyte s. The distal promoter operates in all stages of T cell development, b ut predominates in more mature cells. Both promoters lack a TATAA elem ent and they share little sequence similarity with each other. Using t ransgenic mice to locate in vivo functional cis-acting regions of the murine distal promoter, we defined a region from -1786 to -2913 that i s essential for consistent insertion site-independent expression of a heterologous cDNA reporter. The transgene is lymphoid specific and exp ressed predominantly in T cells. One of four transgenic mice bearing a shortened distal promoter (-886 to +41) expressed the reporter in the expected developmental pattern, suggesting that important regulatory elements that require favorable flanking sequences for expression are present nearer the transcription start site. The DNA sequence from -40 32 to +623 contains few consensus binding sites for previously describ ed T lymphocyte-specific trans-acting factors, and their locations do not correlate well with the functional data. However, the locations of tissue-specific modifications of chromatin structure in the promoter region, manifest as sites of DNase hypersensitivity, correlated with t hese two functional regions in normal mice. The identification of Ick distal promoter regulatory regions provides a useful control element f or deliberate expression of transgenes in mature T lymphocytes. In add ition, these regulatory regions should assist in defining T cell-speci fic trans-acting factors.