Open AccessCold‐Sensitive Ribosome Assembly in an Esclzerichia coli Mutant Lacking a Single Methyl Group in Ribosomal Protein L3
Author(s) -
LHOEST Jacques,
COLSON Charles
Publication year - 1981
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1981.tb06425.x
Subject(s) - ribosome , ribosomal protein , ribosomal rna , 50s , eukaryotic large ribosomal subunit , biology , eukaryotic ribosome , biochemistry , 30s , protein biosynthesis , mutant , methylation , microbiology and biotechnology , escherichia coli , rna , 5s ribosomal rna , dna , gene
Ribosomal protein methylation has been well documented but its function remains unclear. We have examined this phenomenon using an Escherichia coli mutant ( prmB2 ), which fails to methylate glutamine residue number 150 of ribosomal protein L3. This mutant exhibits a cold‐sensitive phenotype: its growth rate at 22°C is abnormally low in complete medium. In addition, strains with this mutation accumulate abnormal and unstable ribosomal particles; 50‐S and 30‐S subunits are formed, but at a lower rate. Once assembled, ribosomes with unmethylated L3 are fully active by several criteria. (a) Protein synthesis in vitro with purified 70‐S prmB2 ribosomes is as active as wild‐type using either a natural (R17) or an artificial [poly(U)] messenger. (b) The induction of β‐galactosidase in vivo exhibits normal kinetics and the enzyme has a normal rate of thermal denaturation. (c) These ribosomes are standard when exposed in vitro to a low magnesium concentration or increasing molarities of LiCl. Efficient methylation of L3 in vitro requires either unfolded ribosomes or a mixture of ribosomal protein and RNA. We suggest that the L3‐specific methyltransferase may qualify as one of the postulated ‘assembly factors’ of the E. coli ribosome.