The human alpha-fetoprotein gene. Sequence organization and the 5' flanking region

The human alpha-fetoprotein (AFP) gene was isolated into three overlapping clones in bacteriophage lambda vectors and its sequence organization analyzed by restriction endonuclease mapping and nucleotide sequencing. The human AFP gene is about 20 kilobase pairs long and contains 15 exons and 14 introns. The overall organization of the human AFP gene is similar to that of the mouse AFP gene, with all but two exons showing identical sizes. Nucleotide sequences at all exon/intron junctions display similarity to the consensus boundary sequence (Breathnach, R., and Chambon, P. (1981) Annu. Rev. Biochem. 50, 349-383), with the GT-AG rule applied to the splicing point. The cap site maps 44 nucleotides upstream from the translation initiation site. The "TATA box" is located 27 nucleotides upstream from the putative cap site and is flanked by sequences with dyad symmetry. The TATA box can thus be placed in the loop portion of a possible stem-loop structure formed by intrastrand base-pairing. Other characteristic nucleotide sequences in the 5' flanking region include a CCAAC pentamer, a 14-base pair (bp) enhancer-like sequence, and a 9-bp sequence homologous to the glucocorticoid responsive element. A long (90 bp) direct repeat and several alternating purine/pyrimidine sequences are also present in the 5' flanking region. A 736-bp sequence of the 5' flanking region adjacent to the cap site of the human AFP gene shows a 61% similarity with the corresponding region of the mouse AFP gene. There are two Alu family sequences and two poly(dT-dG) repeats in the human AFP gene that show different distribution patterns from those in the mouse AFP gene.     

人U_1和U_2 snRNA基因5''''端区域中SV_(40)T抗原结合位点的作用

利用寡聚核苷酸指导的基因定位突变技术,从人U_1和U_2 snRNA基因5'端删去或取代能与SV_(40)T抗原结合的位点,构成基因的缺失和取代突变体。在HeLa细胞核抽提物体外转录系统中,U_1和U_2缺失及取代突变基因与野生型基因有相同的转录水平,而且RNA的合成都是从帽子位点的上游开始的。这意味着基因这一区域的突变不改变其体外转录性质。在人的HeLa和293细胞及蛙卵母细胞中,U_1和U_2缺失突变基因不被转录,而取代突变基因的转录却又恢复到野生型基因水平。这表明人的U_1和U_2基因在这三种细胞内的转录与SV_(40)T抗原结合位点的核苷酸排列顺序无关,而由于结合位点的缺失所造成的空间距离上的变化才是影响转录的主要因素。     

Vertebrate histone genes: nucleotide sequence of a chicken H2A gene and regulatory flanking sequences.

The DNA sequence of a chicken genomal fragment containing a histone H2A gene has been determined. It contains extensive 5' and 3' flanking regions and encodes a protein identical in sequence to the histone H2A protein isolated from chicken erythrocytes. In the 5' flanking region, a possible "TATA box" and three possible "cap sites" can be recognised upstream from the initiation codon. To the 5' side of the "TATA box" is found an unusual sequence of 21 A's interrupted by a central G residue. It occupies the same relative position as the P. miliaris H2A gene-specific 5' dyad symmetry sequence and the "CCAAT box" seen in other eukaryotic polymerase II genes but is clearly different from both. A significant feature of the 3' non-coding region is the presence of a 23 base-pair sequence that is nearly identical to a conserved region found in sea urchin histone genes. The coding region is extremely GC rich, with strong selection for these bases in the third position of codons. Not a single coding triplet ends in U. No intervening sequences were found in this gene.