Genomic structure and chromosomal mapping of the human CD22 gene.
Genomic structure and chromosomal mapping of the human CD22 gene.
复制标题
人类 CD22 基因的基因组结构和染色体作图。
作者：
G. L. Wilson;Vesna Najfeld;E. Kozlow;J. Menniger;D. Ward;J. Kehrl
人CD 22基因在B淋巴细胞中特异性表达，并且可能在细胞-细胞相互作用中具有重要功能。使用接近全长的人CD 22 cDNA克隆来分离跨越CD 22基因的基因组克隆。CD 22基因分布在22 kb的DNA上，由15个外显子组成。第一个外显子包含主要的转录起始位点。翻译起始密码子位于外显子3，其也编码信号肽的一部分。外显子4至10编码CD 22的7个IG结构域，外显子11编码跨膜结构域，外显子12至15编码CD 22的胞浆内结构域，并且外显子15还包含3'非翻译区。次要形式的CD 22 mRNA可能是由外显子5剪接到外显子8，跳过外显子6和7产生的。一个4.6 kb的XbaI片段的CD 22基因被用来映射的染色体位置的CD 22的荧光原位杂交。通过将探针的荧光图像与由Alu探针产生的染色体带型相结合来鉴定杂交位点。结果表明，CD 22位于19号染色体q13.1带区。两个紧密聚集的主要转录起始位点和几个次要起始位点的引物延伸。与许多其他淋巴特异性基因类似，CD 22启动子缺乏明显的TATA盒。对转录起始位点5'端约4kb的DNA进行测序，发现含有多个Alu元件。转录因子NF-κ B、AP-1和Oct-2的潜在结合位点位于主要转录起始位点5'端的300 bp内。将CD 22启动子区的400 bp片段（bp-339至+71）亚克隆到pGEM-氯霉素乙酰转移酶载体中，转染到B和T细胞中后，发现在B和T细胞中均具有活性。对CD 22基因的进一步研究将有助于我们更好地理解CD 22在B细胞发育和分化过程中的表达。
The human CD22 gene is expressed specifically in B lymphocytes and likely has an important function in cell-cell interactions. A nearly full length human CD22 cDNA clone was used to isolate genomic clones that span the CD22 gene. The CD22 gene is spread over 22 kb of DNA and is composed of 15 exons. The first exon contains the major transcriptional start sites. The translation initiation codon is located in exon 3, which also encodes a portion of the signal peptide. Exons 4 to 10 encode the seven Ig domains of CD22, exon 11 encodes the transmembrane domain, exons 12 to 15 encode the intracytoplasmic domain of CD22, and exon 15 also contains the 3' untranslated region. A minor form of CD22 mRNA likely results from splicing of exon 5 to exon 8, skipping exons 6 and 7. A 4.6-kb XbaI fragment of the CD22 gene was used to map the chromosomal location of CD22 by fluorescence in situ hybridization. The hybridization locus was identified by combining fluorescent images of the probe with the chromosomal banding pattern generated by an Alu probe. The results demonstrate that CD22 is located within the band region q13.1 of chromosome 19. Two closely clustered major transcription start sites and several minor start sites were mapped by primer extension. Similarly to many other lymphoid-specific genes, the CD22 promoter lacks an obvious TATA box. Approximately 4 kb of DNA 5' of the transcription start sites were sequenced and found to contain multiple Alu elements. Potential binding sites for the transcriptional factors NF-kappa B, AP-1, and Oct-2 are located within 300 bp 5' of the major transcription start sites. A 400-bp fragment (bp -339 through +71) of the CD22 promoter region was subcloned into a pGEM-chloramphenicol acetyltransferase vector and after transfection into B and T cells was found to be active in both B and T cells. Further studies of the CD22 gene should lead to a greater understanding of the expression of CD22 during B cell development and differentiation.