Max E E, Korsmeyer S J
J Exp Med. 1985 Apr 1;161(4):832-49. doi: 10.1084/jem.161.4.832.
As part of an ongoing investigation of the regulation of gene expression in B cell development, we have obtained a genomic DNA clone encoding the human J chain protein. The nucleotide sequence of exons encoding the mature protein defines a 137 amino acid primary sequence similar to that previously determined at the protein level. Probes from the gene have been used to analyze J chain expression in human cell lines corresponding to pre-B and B lymphocytes. J chain RNA was detected in two of six human pre-B cell lines and in 8 of 10 B cell lines expressing various Ig isotypes. The expression of the J chain gene is, thus, not tightly linked to IgM or IgA secretion. Our data do not, however, support the recent suggestion (7) that synthesis of J chain precedes that of mu chain in B lymphocyte differentiation. Because of the presence of nine candidate polyadenylation signals (AATAAA or AATTAAA) downstream of the C-terminal coding block of the J chain gene, the 3' end of the gene could not be determined from sequence data alone. To define the 3' end, J chain RNA from a human B lymphocyte line was used to protect an end-labelled DNA fragment from S1 nuclease digestion. The sequence 40 basepairs 5' of the functional polyadenylation site identified by these S1 experiments is homologous the same region of a previously reported mouse J chain complementary DNA clone.
作为对B细胞发育过程中基因表达调控正在进行的研究的一部分，我们获得了一个编码人J链蛋白的基因组DNA克隆。编码成熟蛋白的外显子的核苷酸序列确定了一个137个氨基酸的一级序列，与先前在蛋白质水平上确定的序列相似。来自该基因的探针已被用于分析与前B淋巴细胞和B淋巴细胞相对应的人细胞系中的J链表达。在六个前B细胞系中的两个以及十个表达各种Ig同种型的B细胞系中的八个中检测到了J链RNA。因此，J链基因的表达与IgM或IgA的分泌没有紧密联系。然而，我们的数据并不支持最近的建议（7），即在B淋巴细胞分化中J链的合成先于μ链的合成。由于在J链基因的C末端编码区下游存在九个候选聚腺苷酸化信号（AATAAA或AATTAAA），仅从序列数据无法确定该基因的3'末端。为了确定3'末端，使用来自人B淋巴细胞系的J链RNA来保护一个末端标记的DNA片段免受S1核酸酶消化。通过这些S1实验鉴定的功能性聚腺苷酸化位点5'端40个碱基对的序列与先前报道的小鼠J链互补DNA克隆的相同区域同源。
