Rojo F, Weise F, Alonso J C
Centro de Biología Molecular Severo Ochoa, UAM-CSIC, Madrid, Spain.
FEBS Lett. 1993 Aug 9;328(1-2):169-73. doi: 10.1016/0014-5793(93)80987-6.
Genetic evidence suggests that the gene beta product of Streptococcus pyogenes plasmid pSM19035 is required for converting plasmid multimers into monomers. The beta protein was purified from cells overexpressing the cloned gene. N-terminal protein sequence analysis demonstrated that the purified protein had the predicted sequence, except that the N-terminal initiator methionine was not present. Native beta protein consists of a dimer of two identical subunits with a molecular mass of 23.8 kDa (25 kDa in SDS-PAGE). The beta protein (isoelectric point of 9.7) binds specifically to a DNA fragment (312 bp in length) which contains the promoter region of the orf alpha-gene beta operon and two regions (sites I and II) that show dyad axes of symmetry. It is proposed that protein beta binds to sites I and II to mediate resolution of plasmid oligomers.
遗传证据表明，化脓性链球菌质粒pSM19035的基因β产物是将质粒多聚体转化为单体所必需的。β蛋白是从过量表达克隆基因的细胞中纯化得到的。N端蛋白质序列分析表明，纯化后的蛋白质具有预测的序列，只是不存在N端起始甲硫氨酸。天然β蛋白由两个相同亚基组成的二聚体构成，分子量为23.8 kDa（SDS-PAGE中为25 kDa）。β蛋白（等电点为9.7）特异性结合一个DNA片段（长度为312 bp），该片段包含orfα-基因β操纵子的启动子区域以及两个具有二元对称轴的区域（位点I和位点II）。有人提出，β蛋白与位点I和位点II结合以介导质粒寡聚体的拆分。
