Williams J G, Bendig M M, Patient R K, Banville D, Greaves D R, Mahbubani H
Prog Clin Biol Res. 1983;134:27-38.
In the South African clawed toad, Xenopus laevis, the tadpole alpha-globin gene (alpha T1) and the major adult alpha- and beta-globin genes (alpha 1 and beta 1) are linked in the genome in the order alpha T1-alpha 1-beta 1. We show that cloned DNA fragments containing the Xenopus globin genes are replicated after injection into newly fertilized Xenopus eggs, reaching a maximal copy number at gastrulation. The DNA initially replicates as supercoils, but later it is found in a high-molecular-weight form, comigrating with the chromosomal DNA. In contrast to what has been found in mouse eggs, DNA does not become methylated when injected into Xenopus eggs. If, however, DNA is methylated in vitro before injection, methyl groups are retained through replication with a high efficiency. Both the adult alpha 1- and beta 1-globin genes are transcribed from their correct promoters in early embryonic stages, but the amount of transcription is relatively low and decreases in parallel with the decline in the amount of DNA retained in the embryo.
在南非爪蟾（非洲爪蟾）中，蝌蚪α-珠蛋白基因（αT1）以及主要的成体α-和β-珠蛋白基因（α1和β1）在基因组中按αT1-α1-β1的顺序连锁。我们发现，含有非洲爪蟾珠蛋白基因的克隆DNA片段在注入新受精的非洲爪蟾卵后会复制，在原肠胚形成时达到最大拷贝数。DNA最初以超螺旋形式复制，但后来会以高分子量形式存在，与染色体DNA一起迁移。与在小鼠卵中发现的情况相反，注入非洲爪蟾卵中的DNA不会发生甲基化。然而，如果DNA在注射前在体外进行甲基化，甲基基团会在复制过程中高效保留。成体α1和β1珠蛋白基因在胚胎早期阶段均从其正确的启动子转录，但转录量相对较低，并随着胚胎中保留的DNA量的下降而平行减少。
