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 transcription of unrearranged gene segments precedes V(D)J rearrangement, and the correlation between germline transcription and accessibility for recombination is strong; thus it has been suggested that germline transcription may be required for rearrangement. If germline transcription is essential for rearrangement, 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 rearrange, then any promoters which were enhancer dependent might have a transcriptional 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 I(g)H locus, V(H)81X, and to a V(H)J558 gene. Within the V(H)S107 family, the three V(H) genes rearrange with very different relative frequencies, with V1 rearranging the most, and V13 seldom rearranging. We show that only the strong V(H)J558 promoter has 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 promoter has essentially no enhancer-independent activity. In the presence of E(mu), V1 has equivalent activity to J558, while the other promoters show much less activity. Again, 81X is the weakest promoter of all, despite being the 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. Thus, these data show little correlation between the strength or enhancer-independence of these V(H) promoters and the relative frequency of recombination of the corresponding V(H) genes. In addition, the data show that individual V(H) promoters have different strengths even in the presence of E(mu), demonstrating that even promoters within a single V(H) family can be quite heterogeneous.