Mutant Forms of Escherichia coli Protein L25 Unable to Bind 5S rRNA, are Incorporated Efficiently into the Ribosome in vivo
5S rRNA-binding ribosomal proteins of the L25 family are an evolutional feature of bacteria. Earlier we have shown that 1) single replacements in the RNA-binding module of the protein of this family result in destabilization or complete impossibility to form a complex with 5S rRNA in vitro; 2) AL25 ribosomes of Escherichia coli are less efficient in protein synthesis in vivo than the control ribosomes. In the present work we study the efficiency of incorporation of the E. coli protein L25 with mutations in the 5S rRNA-binding region into the ribosome in vivo. It is shown that the mutations in L25 that abolish its ability to form the complex with free 5S rRNA do not prevent its correct and efficient incorporation into the ribosome. This is supported by the fact that even the presence of a very weakly retained mutant form of the protein in the ribosome has a positive effect on the activity of the translational machinery in vivo. All this suggest the existence of an alternative incorporation pathway for this protein into the ribosome, excluding the preliminary formation of the complex with 5S rRNA. At the same time, the stable L25-5S rRNA contact is important for the retention of the protein within the ribosome and the conservative amino acid residues of the RNA-binding module play a key role in this.