Genetic control of ribosome assembly

Abstract

The assembly of E. coli ribosomes has been studied through the analysis of a new group of ribosome maturation mutants. These mutants, all blocked in a late stage in the maturation of 50s ribosomes, map at four different sites on the chromosome. These sites are distant from the known ribosomal protein sites a t the str-aro E region of the chromosome. The ribosome precursor particles of the mutants contain precursor-type 2 3 s RNA (p23 RNA) and 5s RNA. 4 3 s particles of one of the mutants contain all but one of the normal complement of proteins. Precursor 4 3 s particles from this mutant can be converted to particles with sedimentation values around 50s by incubation with extracts from either the wild-type organism or from other mutants. This in vitro conversion process differs considerably from the process of ribosome reconstitution and indicates a role for extrinsic factors in the maturation of E. coli ribosomes. I NTRO DUCT1 ONMany of the important physical-chemical problems that are related t o ribosome function and assembly are being studied by a wide range of technical approaches. In many of these studies the in vitro reconstitution system of Traub and Nomura (1) is an indispensible component. The in vitro reconstitution of 30s ribosomes of Escherichia coli led t o the important notion that ribosomes of bacteria are formed by a self-assembly mechanism. However, this concept may not apply t o the processes which govern ribosome assembly inside the cell.The biosynthesis o f ribosomes in vivo requires the participation o f a large number of gene products: the genes for structural components ( 3 different RNA molecules and 55 different proteins) as well as the genes which specify a variety of RNA nucleotide methylases, RNA trimming enzymes and at least one enzyme that acetylates a protein of 166 0 1974 Alan R.

Effects of Detergents on Ribosomal Precursor Subunits of Bacillus megaterium

“…DISCUSSION We previously reported (1) that various methods of cell disruption and/or the use of DOC can alter the physical properties of ribosomal precursor subunits. The data presented in this study indicated that another detergent, LOC, which has been used by Bryant and Sypherd in studies of ribosome assembly (3,19), also alters the sedimentation properties of ribosomal precursor subunits as well as mature 30S subunits ( Fig. 2A).…”