Aguado B, Campbell R D
Department of Biochemistry, University of Oxford, United Kingdom.
Genomics. 1995 Feb 10;25(3):650-9. doi: 10.1016/0888-7543(95)80007-9.
Recent characterization of the class III region of the human major histocompatibility complex (MHC), located in chromosome 6p21.3, has revealed that it is very gene dense and contains at least 47 transcriptional units. One of these is the gene G17, which lies 250 kb telomeric of the class II gene DRA. DNA sequence analysis of 5.5 kb of DNA corresponding to the G17 gene has revealed that it encodes PBX2, a homeodomain-containing protein with extensive similarity to PBX1 (which is involved in t(1;19) chromosomal translocations in acute pre-B-cell leukemias). Comparison of the genomic DNA sequence with the published PBX2 cDNA sequence, which are 99.7% identical, indicates that the G17 gene is split into 9 exons, with the intron/exon boundaries conforming to the normal pattern (AG/.../GT) for splice sites. Of the 9 differences observed between the PBX2 cDNA sequence and the G17 genomic sequence, only 1 is contained in the coding sequence and alters the derived amino acid sequence. This results in an Ile (PBX2)-Met (G17) substitution at amino acid 393 near the C-terminus. The PBX2 gene was originally localized only to human chromosome 3q22-q23. However, comparison of genomic and cosmid Southern blots clearly indicates that another copy(ies) of the PBX2 (G17) gene exist(s) in the genome. PCR amplification of exons III and IX of the G17 (PBX2) gene, corresponding to the coding and 3' untranslated regions, respectively, using as template genomic DNA from a panel of monochromosomal somatic human-rodent cell hybrids, gave specific products in hybrids that contain human chromosomes 6, 3, and 1. These results confirm that copies of the PBX2 gene are located on human chromosomes 6 and 3 and indicate that a gene homologous to PBX2 could exist on human chromosome 1. Further PCR analysis of the genes and reverse transcribed mRNA from the hybrid cell lines has revealed that the copies of the PBX2 gene on human chromosomes 6 and 1 are expressed, while the copy on human chromosome 3 may be a processed pseudogene.
人类主要组织相容性复合体（MHC）Ⅲ类区域位于6号染色体p21.3，近期对该区域的特征分析表明，它基因密度很高，至少包含47个转录单位。其中一个是G17基因，它位于Ⅱ类基因DRA端粒方向250 kb处。对与G17基因对应的5.5 kb DNA进行的DNA序列分析表明，它编码PBX2，一种与PBX1具有广泛相似性的含同源结构域蛋白（PBX1参与急性前B细胞白血病中的t(1;19)染色体易位）。将基因组DNA序列与已发表的PBX2 cDNA序列进行比较（二者一致性为99.7%），结果表明G17基因被分成9个外显子，内含子/外显子边界符合剪接位点的正常模式（AG/.../GT）。在PBX2 cDNA序列与G17基因组序列之间观察到的9个差异中，只有1个存在于编码序列中，并改变了推导的氨基酸序列。这导致在靠近C端的第393位氨基酸处发生异亮氨酸（PBX2）-甲硫氨酸（G17）的替换。PBX2基因最初仅定位于人类3号染色体q22-q23。然而，基因组和黏粒Southern杂交分析清楚地表明，PBX2（G17）基因在基因组中存在另一个拷贝。以一组单染色体体细胞人-鼠细胞杂种的基因组DNA为模板，分别对G17（PBX2）基因的外显子Ⅲ和Ⅸ进行PCR扩增，外显子Ⅲ和Ⅸ分别对应编码区和3'非翻译区，在含有人类6号、3号和1号染色体的杂种细胞中得到了特异性产物。这些结果证实PBX2基因的拷贝位于人类6号和3号染色体上，并表明在人类1号染色体上可能存在与PBX2同源的基因。对杂种细胞系中的基因和逆转录mRNA进行的进一步PCR分析表明，人类6号和1号染色体上的PBX2基因拷贝是表达的，而人类3号染色体上的拷贝可能是一个加工过的假基因。
