THE ROLES OF PROTEINS L28 AND L33 IN THE ASSEMBLY AND FUNCTION OF ESCHERICHIA-COLI RIBOSOMES IN-VIVO

Strain BM108 of Escherichia coli has a chromosomal mutation in the rpm B,G operon that prevents synthesis of ribosomal proteins L28 and L33. The mutation was lethal unless synthesis of protein L28 was induced fr om a plasmid. Without protein L28, RNA and protein synthesis were line ar rather than exponential. No 70S ribosomes were made. Instead, RNA a ccumulated in '30S material' and '47S particles'; the latter were dist inct from 50S ribosomal subunits, lacked proteins L28 and L33 and had substoicheometric amounts of three other proteins. When L28 synthesis was induced (but protein L33 was still absent), the strain grew as wel l as, and assembled 70S ribosomes with similar kinetics to, a wild-typ e control. Thus, protein L28 is required for ribosome assembly in stra in BM108 while protein L33 has no significant effect on ribosome synth esis or function.