Onisto M, Zeilante P, Scannapieco P, Pellati D, Pozza M, Caenazzo C, Negro A, Garbisa S
Medical School, Department of Biological Chemistry, University of Padua, viale G. Colombo 3, Padua, 35121, Italy.
Exp Cell Res. 1998 Aug 1;242(2):451-9. doi: 10.1006/excr.1998.4074.
A novel 44-kDa gene product (D123) has been proposed as necessary for S-phase entry of the cell cycle: a point mutation resulted in a temperature-sensitive arrest in G1-phase. From human fibrosarcoma cDNA library, we have isolated an identical gene and studied its sequence and mRNA and protein expression. Compared with D123, three nucleotide differences within the human coding sequence, plus others, result in a change of two amino acids. A partial sequence similarity has been found with a yeast gene of unknown function. The protein has several potential phosphorylation sites, is highly hydrophilic, and may be highly structured in alpha-helix. The mRNA is abundantly expressed by a variety of normal and transformed cells and by all tissues examined, being most highly expressed in testis. Specific antibodies, raised against a rhD123 polypeptide, recognize a major 42- to 44-kDa molecule in crude extract of various human cell lines. Immunohistochemistry reveals that D123 protein is not homogeneously expressed: it is detected, often in granular vescicles, in the cytoplasm of some epithelial, stromal, and sperm cells and in varicosities lining nervous fibers, while it appears to be absent in nuclei, endothelial, and smooth muscle cells. The precise link between cytoplasmic occurrence of D123 and cell cycle progression still remains to be clarified.
一种新的44 kDa基因产物（D123）被认为是细胞周期进入S期所必需的：一个点突变导致在G1期出现温度敏感性停滞。我们从人纤维肉瘤cDNA文库中分离出了一个相同的基因，并研究了其序列以及mRNA和蛋白质表达情况。与D123相比，人类编码序列内有三个核苷酸差异以及其他差异，导致两个氨基酸发生变化。已发现与一个功能未知的酵母基因存在部分序列相似性。该蛋白质有几个潜在的磷酸化位点，具有高度亲水性，并且可能在α螺旋中具有高度结构。该mRNA在多种正常细胞和转化细胞以及所有检测的组织中大量表达，在睾丸中表达最高。针对重组人D123多肽产生的特异性抗体，能识别各种人类细胞系粗提物中的一个主要的42至44 kDa分子。免疫组织化学显示，D123蛋白的表达并不均匀：在一些上皮细胞、基质细胞和精子细胞的细胞质中，以及神经纤维内衬的静脉曲张中经常能检测到，通常呈颗粒状囊泡形式，而在细胞核、内皮细胞和平滑肌细胞中似乎不存在。D123在细胞质中的出现与细胞周期进程之间的确切联系仍有待阐明。
