The Nature of the Proteins Present in the 'Relaxed Particles' from Methionine-starved Escherichia coli A19 (Hfr rel met rns)

Abstract

The ' relaxed particles ' formed during methionine starvation of Escherichia coli A I~ (Hfr re1 met rns) have been isolated by large-scale rate-zonal density gradient ultracentrifugation. The proteins and rRNA species associated with these particles have been examined.The rRNA species present are precursor and mature forms of I 6 S and 23 S rRNA. The bulk of the rRNA which accumulates during starvation is found within the particles. The proteins prepared directly from the particles give strong multiple immunoprecipitates with antisera specific to 30 S and 50 S ribosomal proteins. The soluble proteins, prepared and examined in the same manner, do not give this immunological reaction. Two-dimensional electrophoresis patterns of the proteins from the particles show that the proteins co-migrate with proteins from 30s and 50s ribosomes and are entirely dissimilar to the proteins prepared by the same methods from the soluble fraction of the cells. On the basis of these and other observations, it is concluded that the 'relaxed particles' are not artefacts but are arrested ribosome precursors containing both rRNA and certain ribosomal proteins.The free pool of ribosomal proteins is low in exponential-phase cells and is not significantly increased by a 2 h period of starvation for glucose.The implications of these observations concerning the proteins associated with 'relaxed' and 'chloramphenicol particles' are discussed in relation to ribosome biogenesis and the stabilization of rRNA.

Interactions between Mutations Affecting Ribosome Synthesis in Escherichia coli

“…The sedimentation profiles show that much of the [ 3H]RNA synthesized during starvation of transductant RE74-803 was in two components located on either side of the 30s sub-units. These sedimentation characteristics are similar to those of 'relaxed particles' that contain precursor forms of ribosomal RNA and are synthesized by other relaxed strains during amino acid starvation (Sykes et al, 1977). Most of the RNA made during starvation of transductant RE74-807 (and transductant RE74-825) was in particles with very similar sedimentation properties, although in rather different proportions.…”

The Nature of the Proteins in 'Chloramphenicol Particles' from Escherichia coli A19 (Hfr rel met rns)

“…3f). The rRNA preparations from PI and to a lesser extent P2 invariably showed evidence of breakdown of the RNA which was not observed in the simultaneous preparation from P3 or the corresponding preparation from methionine-starved cells (Sykes, Metcalf & Pickering, 1977). The proportion of mr6S rRNA is greater in P2 than P3 and in the latter, which encompasses the 30s ribosome region, there is no evidence of p16S rRNA and m16S rRNA is the dominant species.…”

Authentic precursors to ribosomal subunits accumulate in Escherichia coli in the absence of functional DnaK chaperone

“…In the past, various treatments of E. coli cells and a large number of mutations in ribosomal as well as in non‐ribosomal (see the more recent study by Charollais et al ., 2003) components have been shown to cause the accumulation of ribosomal particles. Whether these particles are true intermediates has been the subject of some controversy (Sykes et al ., 1977; Nomura, 1990). In our case, a careful analysis of the ribosomal precursor particles that accumulate in the absence of functional DnaK shows that they are similar to those found in normal E. coli cells, in terms of their sedimentation values and ribosomal protein and rRNA composition (Hayes and Hayes, 1971; Nierhaus et al ., 1973; Turco et al ., 1974; Lindahl, 1975; Pichon et al ., 1975; Butler et al ., 1980).…”