Shafferman A, Flashner Y, Hertman I, Lion M
Mol Gen Genet. 1987 Jun;208(1-2):263-70. doi: 10.1007/BF00330452.
The functional R6K alpha origin is composed of two DNA elements, one of 580 bp carrying the alpha origin sequences and the other of 277 bp containing the seven 22 bp direct repeats previously identified as also required for gamma and beta origin activity. These two genetic elements are separated by approximately 3,000 bp of R6K sequences which are dispensable for alpha origin activity. The function of the alpha origin depends on the presence in cis of the 580 bp and the 277 bp fragments and requires that they be oriented as in the intact R6K. Activation of the alpha origin depends on the R6K replication initiation protein pi. Within the 580 bp of the alpha origin, there is a sequence of 98 bp which appears as an inverted repeat of 96 bp in the beta replicon. Deletion of the 96 bp or 98 bp results in inactivation of the alpha and the beta origins respectively. These long repeats are palindromic and it is suggested that these may serve as the recognition signals for initiation of DNA replication in the alpha and the beta origins of R6K. DNA homology analysis performed on alpha, beta and gamma origin sequences, also reveals 10-23 bp sequences in the alpha and the beta origins that are related to the family of 22 bp direct repeats in the gamma origin which were shown previously to be binding sites for the pi protein.
功能性R6Kα 起始位点由两个DNA元件组成，一个是580 bp的元件，携带α 起始位点序列，另一个是277 bp的元件，包含先前确定的对γ 和β 起始位点活性也必需的七个22 bp直接重复序列。这两个遗传元件被大约3000 bp的R6K序列隔开，这些序列对α 起始位点活性是可有可无的。α 起始位点的功能取决于580 bp和277 bp片段在顺式中的存在，并且要求它们的方向与完整R6K中的方向一致。α 起始位点的激活取决于R6K复制起始蛋白π。在α 起始位点的580 bp内，有一个98 bp的序列，它在β 复制子中表现为96 bp的反向重复序列。删除96 bp或98 bp分别导致α 和β 起始位点失活。这些长重复序列是回文的，有人认为它们可能作为R6K的α 和β 起始位点DNA复制起始的识别信号。对α、β 和γ 起始位点序列进行的DNA同源性分析还揭示，α 和β 起始位点中有10 - 23 bp的序列与γ 起始位点中22 bp直接重复序列家族相关，先前已证明这些序列是π 蛋白的结合位点。
