Hiraga S, Niki H, Imamura R, Ogura T, Yamanaka K, Feng J, Ezaki B, Jaffé A
Department of Molecular Genetics, Kumamoto University Medical School, Japan.
Res Microbiol. 1991 Feb-Apr;142(2-3):189-94. doi: 10.1016/0923-2508(91)90029-a.
Recent experimental results suggest that replicated daughter chromosomes (nucleoids) in Escherichia coli move non-progressively and abruptly at an early stage of the D (division) period from midcell toward the cell quarter positions, which will become the centres of the daughter cells. The chromosome positioning at the quarter positions was found to be controlled by the muk gene products. In muk mutants, normal size anucleate cells are spontaneously produced during cell division. The mukA gene is identical to the tolC gene encoding an outer membrane protein. The mukB gene codes for a 177-kDa protein. The amino acid sequence of the MukB protein deduced for the nucleotide sequence suggests that the MukB protein has five characteristic secondary structure domains: an amino-terminal globular domain containing a consensus sequence binding with ATP or another nucleotide. The central region of the protein consists of two alpha-helical coiled-coil domains and one globular domain. A carboxyl-terminal globular domain is rich in cysteine and positively charged residues arginine and lysine. Two MukB protein molecules might form a homodimer in the coiled-coil regions. The predicted secondary structure of the MukB protein suggests that the protein provides the force required for the positioning of nucleoids from midcell toward the cell quarters. The mukC and mukD genes are located at 88 and 41 min of the chromosome map, respectively.
最近的实验结果表明，大肠杆菌中复制后的子染色体（类核）在D（分裂）期早期从细胞中部向细胞四分之一位置进行非渐进性且突然的移动，这些位置将成为子细胞的中心。已发现染色体在四分之一位置的定位受muk基因产物控制。在muk突变体中，细胞分裂期间会自发产生正常大小的无核细胞。mukA基因与编码外膜蛋白的tolC基因相同。mukB基因编码一种177 kDa的蛋白质。根据核苷酸序列推导的MukB蛋白的氨基酸序列表明，MukB蛋白具有五个特征性二级结构域：一个氨基末端球状结构域，含有与ATP或另一种核苷酸结合的共有序列。该蛋白的中心区域由两个α螺旋卷曲螺旋结构域和一个球状结构域组成。羧基末端球状结构域富含半胱氨酸以及带正电荷的精氨酸和赖氨酸残基。两个MukB蛋白分子可能在卷曲螺旋区域形成同型二聚体。MukB蛋白预测的二级结构表明，该蛋白为类核从细胞中部向细胞四分之一位置的定位提供所需的力。mukC和mukD基因分别位于染色体图谱的88和41分钟处。
