A cloned human immunoglobulin heavy chain gene with a novel direct-repeat sequence in 5' flanking region

Abstract

A rearranged human immunoglobulin γ 1 heavy-chain gene (HIG1) was cloned from a human plasma cell leukemia cell line, ARH-77. The cloned gene possessed a unique direct repeat sequence of 84 bp in the 5' flanking region as well as an enhancer-like element in the J H-C γ1 intron. The latter sequence is located 1 kb downstream of 3' end of the J 6 exon. The direct-repeat sequence in the 5' -flanking region contained a core-like sequence resembling that of viral enhancer elements. It is located in the intron between two leader exons. P1 nuclease mapping and exonuclease VII digestion experiments showed that most of the direct repeats are noncoding regions and spliced out from the transcript. These data suggested that HIG1 gene might have two kinds of enhancer-like elements at both sides of the V region gene. HIG1 gene has been introduced by the protoplast fusion into mouse myeloma cells (NSI and J558L cells) and mouse fibroblasts. A pSV2 gpt vector containing HIG1 gene (pSV2-HIG1) was used to transform the cells. The amounts of mRNA synthesized in the transformed cells were at least 50 to 100 times larger than those in ARH-77 cells, although about one copy of HIG1 gene was present in DNA of a transformed cell. HIG1 gene was not expressed in fibroblasts, indicating that the enhancer of HIG1 gene acts in a tissue-specific manner but not in a species-specific one. The role of two kinds of enhancer-like elements in HIG1 gene is discussed in connection with the high-level expression of this gene in mouse myeloma cells.