FUNCTIONAL-ANALYSIS OF THE V-GAMMA-3 PROMOTER OF THE MURINE GAMMA-DELTA T-CELL RECEPTOR

The initial day 14 wave of fetal thymocytes express a gammadelta T-cel l receptor (TCR). This surface TCR is generated by preferential rearra ngement of Vgamma3 and Vdelta1 recombination segments. To delineate th e role of regulatory sequences in this expression, we have analyzed th e Vgamma3 promoter control region under the regulation of its cognate Cgamma1 enhancer. Transcription initiates 25 bases downstream from a T ATTAA sequence at a consensus initiator motif. The minimal 5' promoter sequences supporting expression by transient analysis extend -243 nuc leotides from the +1 start site. Three regulatory sequences in this re gion have been defined by deletion and mutagenesis: a consensus CTF/NF -1 site at -55, an Ets homology sequence at -65, and a degenerate, but crucial, SP-I site at -100. The presence of additional sequences down stream of the start site which extend through the leader intron were n ecessary for expression. In contrast to other TCR or immunoglobulin va riable regions, one or more strong upstream suppressor sequences resem bling silencer elements have been observed. A 311-bp fragment, positio ns -586 to -897, exhibited strong repressing activity regardless of or ientation when placed upstream of heterologous promoters.