摘要
The in vivo assembly of ribosomal subunits is a highly complex process, with a tight coordination between protein assembly and rRNA maturation events, such as folding and processing of rRNA precursors, as well as modifications of selected bases. In the cell, a large number of factors are required to ensure the efficiency and fidelity of subunit production. Here we characterize the immature 30S subunits accumulated in a factor-null Escherichia coil strain （ArsgAArbfA）. The immature 30S subunits isolated with varying salt concentrations in the buffer system show interesting differences on both protein composition and structure. Specifically, inter- mediates derived under the two contrasting salt condi- tions （high and low） likely reflect two distinctive assembly stages, the relatively early and late stages of the 3＇ domain assembly, respectively. Detailed structural analysis demonstrates a mechanistic coupling between the maturation of the 5＇ end of the 17S rRNA and the assembly of the 30S head domain, and attributes a unique role of S5 in coordinating these two events. Furthermore, our structural results likely reveal thelocation of the unprocessed terminal sequences of the 17S rRNA, and suggest that the maturation events of the 17S rRNA could be employed as quality control mech- anisms on subunit production and protein translation.
The in vivo assembly of ribosomal subunits is a highly complex process, with a tight coordination between protein assembly and rRNA maturation events, such as folding and processing of rRNA precursors, as well as modifications of selected bases. In the cell, a large number of factors are required to ensure the efficiency and fidelity of subunit production. Here we characterize the immature 30S subunits accumulated in a factor-null Escherichia coil strain （ArsgAArbfA）. The immature 30S subunits isolated with varying salt concentrations in the buffer system show interesting differences on both protein composition and structure. Specifically, inter- mediates derived under the two contrasting salt condi- tions （high and low） likely reflect two distinctive assembly stages, the relatively early and late stages of the 3＇ domain assembly, respectively. Detailed structural analysis demonstrates a mechanistic coupling between the maturation of the 5＇ end of the 17S rRNA and the assembly of the 30S head domain, and attributes a unique role of S5 in coordinating these two events. Furthermore, our structural results likely reveal thelocation of the unprocessed terminal sequences of the 17S rRNA, and suggest that the maturation events of the 17S rRNA could be employed as quality control mech- anisms on subunit production and protein translation.
