Rohrbaugh M L, Johnson J E, James M D, Hardison R C
Mol Cell Biol. 1985 Jan;5(1):147-60. doi: 10.1128/mcb.5.1.147-160.1985.
We have hybridized pulse-labeled nuclear transcripts to cloned DNA fragments from the rabbit beta-like globin genes to determine the developmental timing, extent, and asymmetry of their transcription. The fetal-adult gene beta 1 was transcribed in fetal liver but not embryonic nuclei, whereas genes beta 3 and beta 4, which encode embryonic globin polypeptides, were transcribed only in embryonic nuclei. This shows that the switch from embryonic to fetal-adult globin production in rabbits is accomplished primarily by differential transcription of the beta-like globin genes. Gene beta 1 was subdivided into M13 subclones and tested for hybridization to nascent RNA. The nucleotide sequence of the 3' flanking region of gene beta 1 was also determined for 2,447 base pairs past the polyadenylation [poly(A)] site. No transcripts were found 5' to the cap site, but asymmetric transcription of gene beta 1 proceeded at a high level through the gene and past the poly(A) addition site for 603 nucleotides. The level of transcription declined after this, gradually dropping through the next 568 nucleotides. No polymerases were found on a fragment that begins 1,707 nucleotides past the poly(A) site; this fragment was part of a segment of repetitive DNA. These data show that the transcription unit of gene beta 1 begins at or near the cap nucleotide and extends at least 1,171 but no more than 1,706 nucleotides past the poly(A) addition site. The DNA segment that precedes the region of declining transcription contained an inverted repeat and encoded a short RNA transcribed by RNA polymerase II from the strand opposite the beta 1 transcript. These two features may function to attenuate the transcription of gene beta 1. An inverted repeat and a potential polymerase II transcription unit were also found in the homologous segment 3' to the human beta-globin gene. A short DNA segment close to the 3' end of the beta 1 transcription unit was transcribed more actively than the surrounding DNA, and it contained sequences that match the consensus internal control region for RNA polymerase III. This DNA segment may contain a separate polymerase III transcription unit. A member of the D repeat family located 3' to gene beta 1 was not transcribed in its entirety coordinately with beta 1.
我们已将脉冲标记的核转录本与兔β样珠蛋白基因的克隆DNA片段进行杂交，以确定其转录的发育时间、程度和不对称性。胎儿-成人基因β1在胎儿肝脏中被转录，但在胚胎细胞核中不被转录，而编码胚胎珠蛋白多肽的基因β3和β4仅在胚胎细胞核中被转录。这表明兔子从胚胎珠蛋白产生向胎儿-成人珠蛋白产生的转变主要是通过β样珠蛋白基因的差异转录来实现的。基因β1被细分为M13亚克隆，并测试其与新生RNA的杂交情况。还确定了基因β1的3'侧翼区域在多聚腺苷酸化[poly(A)]位点之后2447个碱基对的核苷酸序列。在帽位点5'端未发现转录本，但基因β1的不对称转录在整个基因中高水平进行，并在多聚(A)添加位点之后持续603个核苷酸。在此之后转录水平下降，在接下来的568个核苷酸中逐渐降低。在多聚(A)位点之后1707个核苷酸开始的片段上未发现聚合酶；该片段是重复DNA片段的一部分。这些数据表明基因β1的转录单位始于帽核苷酸处或其附近，并在多聚(A)添加位点之后延伸至少1171个但不超过1706个核苷酸。转录水平下降区域之前的DNA片段包含一个反向重复序列，并编码由RNA聚合酶II从与β1转录本相反的链转录的短RNA。这两个特征可能起到减弱基因β1转录的作用。在人β珠蛋白基因3'端的同源片段中也发现了一个反向重复序列和一个潜在的聚合酶II转录单位。靠近β1转录单位3'端的一个短DNA片段比周围DNA转录更活跃，并且它包含与RNA聚合酶III的共有内部控制区域匹配的序列。该DNA片段可能包含一个单独的聚合酶III转录单位。位于基因β1 3'端的D重复家族成员并非与β′1完全协调转录。
