Transcription of germline VH gene elements by normal human fetal liver.

Transcription of the gene elements that form the variable region of immunoglobulin heavy chains has been proposed to represent the process that controls access for the recombination enzymes in their sequential steps of catalysis. Evidence for germline transcription of VH gene elements, as part of VH to DJH recombination, has been limited to transcripts of only a few gene elements. We have examined normal fetal liver mRNA by Northern blotting and present evidence for germline transcripts from six human VH gene families. The candidate VH4 transcripts have been confirmed as germline transcripts by hybridization with 3' flanking sequences that would have been removed by recombination from mature VHDJH genes. The candidate transcripts for VH1, VH3, VH4 and VH6 have been confirmed by polymerase chain reaction amplification with primers from the 3' flanking sequences of these gene families and determination of the sequence of these products. Determination of sequence from two clones of VH1, VH3 and VH4 indicates that more than one gene from each of these families is transcribed. PCR amplification of VH4 and VH6 with primers specific for the leader sequence (exon 1) and 3' flanking sequence indicate that these transcripts are spliced, representing RNA processing. Germline transcripts from these families are also present in normal human bone marrow. These results indicate that transcriptional activation of germline VH gene elements is a general phenomenon in tissues undergoing V to DJ recombination.