Individual V-H promoters vary in strength, but the frequency of rearrangement of those V-H genes does not correlate with promoter strength nor enhancer-independence

The process of V(D)J recombination is highly regulated. Germline transcript ion of unrearranged gene segments precedes V(D)J rearrangement, and the cor relation between germline transcription and accessibility for recombination is strong; thus it has been suggested that germline transcription may be r equired for rearrangement. If germline transcription is essential for rearr angement, then the level of transcription of individual gene segments might affect the relative frequency of recombination of those genes. Also, since the intronic enhancer, E mu. is very distant from V-H genes before they re arrange, then any promoters which were enhancer dependent might have a tran scriptional advantage. Here we study in luciferase vectors the promoters of three functional genes of the V(H)S107 family, and compare them to that of the most frequently rearranging gene in the mouse IgH locus, V(H)81X, and to a V(H)J558 gene. Within the V(H)S107 family, the three V-H genes rearran ge with very different relative frequencies, with V1 rearranging the most, and V13 seldom rearranging. We show that only the strong VHJ558 promoter ha s significant luciferase reporter gene activity in the absence of E mu. V1 has only 20% as much activity as J558 in the absence of E mu, and the other promoters have less than 8% of the activity of J558. Notably, the 81X prom oter has essentially no enhancer-independent activity. In the presence of E mu, V1 has equivalent activity to J558, while the other promoters show muc h less activity. Again, 81X is the weakest promoter of all, despite bring t he most frequently rearranging gene. Finally, we show that the steady state level of V(H)S107 and V(H)7183 germline transcripts in vivo is very low. T hus, these data show little correlation between the strength or enhancer-in dependence of these V-H promoters and the relative frequency of recombinati on of the corresponding V-H genes. In addition, the data show that individu al V-H promoters have different strengths even in the presence of E mu demo nstrating that even promoters within a single V-H family can be: quite hete rogeneous. (C) 2000 Elsevier Science Ltd. All rights reserved.