Two purified factors bind to the same sequence in the enhancer of mouse MHC class I genes: one of them is a positive regulator induced upon differentiation of teratocarcinoma cells

The MHC class I murine and beta-2-microglobulin genes are silent in embryonal carcinoma (EC) cells but are induced upon differentiation of these cells. We have previously shown that enhancer-like sequences located in the promoter of the H-2Kb gene are non-functional in F9 and PCC3 cells. We have previously purified a 48 kd protein (KBF1) from a mouse T cell line which binds to a palindromic sequence located in this enhancer and to a similar sequence in the promoter of the beta-2-microglobulin gene. We describe here the purification of a second protein (KBF2, 58 kd) which also binds to this sequence. While both activities are present in differentiated cells, KBF1 binding activity is absent in undifferentiated EC cells, where the palindromic sequence shows no enhancer activity. Upon differentiation, KBF1 binding activity is induced and the palindromic sequence becomes active as an enhancer. Thus, the absence of KBF1 activity in undifferentiated EC cells is at least in part responsible for the lack of expression of H-2 class I and beta-2-microglobulin genes in these cells and suggests that KBF1 activity is regulated during differentiation.     

AchR亚基基因启动子与分化/未分化肌细胞核因子的相互作用分析

采用凝胶阻滞实验比较分析了鸡烟碱样乙酰胆碱受体（ＡＣｈＲ）亚基基因－２７５／＋３６片段与分化／未分化肌细胞核抽提物的相互作用．发现未分化肌细胞核内存在两种直接识别ＡＣｈＲ启动子的结合活性,其结合反应不能被ＡＣｈＲα亚基基因增强子（含Ｅ盒子）竞争阻断,揭示此结合活性与ＭｙｏＤ家族无关,并表现为基因特异性结合;两种结合活性中一种结合活性既存在于未分化细胞,也存在于分化肌细胞,另一种结合活性只存在于未分化肌细胞．存在于未分化肌细胞、特异识别基因的结合活性不同于ＭｙｏＤ家族,也不同于已发现的Ｉｄ和Ｉ－ｍｆ（两者不能直接结合ＤＮＡ）,可能与基因在未分化肌细胞中表达的负调控有关．     

Expression of various viral and cellular enhancer-promoters during differentiation of human embryonal carcinoma cells

Alterations in the pattern of gene expression were studied during differentiation of the human embryonal carcinoma (EC) cell line NEC14. NEC14 cells can be induced to differentiate by the addition of 10(-2) M N,N'-hexamethylene-bis-acetamide (HMBA). The efficiency of DNA transfection of undifferentiated and differentiated NEC14 cells was compared by measuring the activities of endogenous and exogenously introduced promoters for the beta-actin gene and heat shock protein 70 gene. The results indicated that the efficiency was not significantly different in cells of these two states. Under the conditions used, all the viral enhancer-promoters tested showed very little or no activity in undifferentiated cells, but activities of SV40, BKV, adenovirus and RSV enhancers were greatly increased after differentiation. Activities of these viral enhancers in differentiated cells were completely repressed by cotransfection with the adenovirus E1A gene. An E1A-inducible promoter of the adenovirus E2 gene showed stronger activity in differentiated than in undifferentiated cells, and was not activated efficiently by cotransfection with the E1A gene in either undifferentiated or differentiated cells. These results indicate that factor(s) regulating activities of various enhancer-promoters in NEC14 cells is or are different from E1A-like factor(s) present in mouse EC F9 cells.     

雌性畸胎瘤细胞离体分化时X染色体的行为

用雌性畸胎瘤LT细胞(具有两个X染色体)为材料,在离体条件下诱导分化。通过对X连锁的HPRT和G6PD等酶的定量分析,并与Pcc3/A/1畸胎瘤细胞(XO型)对比。结果表明,HPRT与G6PD酶比活性在分化后的LT细胞中,以及在已分化的胚胎体重新种植并传代后的细胞中,均与Pcc3/A/1(XO型)细胞相似,比未分化的细胞降低了一半左右。这些结果可认为,在雌性畸胎瘤细胞离体分化过程中,发生了X染色体的生化分化。