PROMOTER SEQUENCES FOR THE ESTABLISHMENT OF MEC-3 EXPRESSION IN THE NEMATODE CAENORHABDITIS-ELEGANS

In certain stereotyped lineages of Caenorhabditis elegans, the mec-3 g ene is transcribed in neurons that are anterior daughters of cells con taining the UNC-86 protein. UNC-86 binds to the mec-3 promoter and is necessary for transcription activation, but this protein is present in many cells that do not transcribe mec-3, including the posterior sist er and parent cells of the mec-3-expressing neurons. To understand how the mec-3 promoter directs transcription in only a subset of cells th at contain UNC-86, we have compared sequences within the promoter that are bound by UNC-86 in vitro with sequences that are necessary for ea rly transcription of mec-3 in vivo. We find that upstream of the mec-3 start codon are two blocks of sequence that are each sufficient to ge nerate the cellular pattern of mec-3 transcription. The proximal seque nce includes three previously identified short regions that have been conserved in nematode evolution and each contains one high-affinity UN C-86 binding site. The recognition consensus sequence for UNC-86 is CA Tnnn(T)/(A)AAT, which is identical to the recognition sequence for the UNC-86-related mammalian transcription factor Brn-3. Adjacent to the UNC-86 recognition site is an additional sequence that is important fo r establishment of mec-3 expression and is presumably recognized by an unidentified transcription factor.