Interconnection between assembly and synthesis of ribosomal proteins

DNA sequence and complementation analysis of a mutation in the rplX gene from Escherichia coli leading to loss of ribosomal protein L24

A mutation in Escherichia coli leads to the loss of ribosomal protein L24, severely impaired growth, and a temperature-sensitive phenotype. The mutation was shown to be in rplX, the gene for protein L24, and was due to the alteration of an AAA codon to a TAA stop codon at position 61 in rplX that resulted in a 20-amino acid peptide instead of the 104 amino acids of wild-type L24 protein. rplX genes from three temperature-resistant and fast growing pseudorevertants of the mutant were cloned and sequenced. They were found to have different base substitutions in the TAA codon, resulting in the reappearance of a full-sized protein L24 moiety. Complementation of the slow growth in trans could be achieved with several plasmids containing at least the spc promoter and intact L14 and L24 genes. Plasmids containing genes distal to rplX could further stimulate growth, and the wild type arose when the entire spc operon and the alpha operon were present. In all cases, protein L24 was expressed by the plasmids. Therefore, slow growth could be explained by polarity extending to the alpha operon. However, temperature sensitivity could not be complemented by any of the plasmids in trans, although we found that this phenotype was caused by the mutation in the rplX gene.

Insertion of IS1 into the rpsE gene for ribosomal protein S5 causes cold-sensitivity in Escherichia coli

The nucleotide sequence of the rpsE gene for the ribosomal protein S5 of a mutant of E. coli showing cold-sensitive growth revealed the presence of an insertion sequence, IS1, near the 3'-end of the gene. This mutant grows very slowly even at the "permissive temperature" (30 degrees C). At temperatures below 20 degrees C, its growth becomes negligible. It is likely that the presence of IS1 disturbs the continued translation of the polycistronic messenger RNA of the "spc-operon" from the point of IS1 insertion downwards, especially at the unfavorable temperatures.