Regulation of ribosomal protein synthesis in Escherichia coli by selective mRNA inactivation.

Abstract

In an Escherichia coli strain lysogenic for Xspc2 transducing phage, an extra copy of ribosomal protein (r-protein) genes in the spc and a operons are carried on the phage chromosome. Expression of genes in the spc operon in this merodiploid strain was compared with that in a control "haploid" strain carrying XtrkA phage. It was found that the synthesis rate of spc mRNA, relative to other reference mRNA in the merodiploid strain, is about 2-fold higher than that in the control strain; yet, no dosage effect was observed in the synthesis rate of r-proteins in the spc or a operon. The spc mRNA was found to be more rapidly degraded in the merodiploid strain than in the control strain, and its steady-state amount, relative to reference mRNA, was only slightly higher in the merodiploid strain than in the control strain. Thus, E. coli cells have the ability to regulate the rate of r-protein synthesis regardless of the rate of transcription of r-protein genes, presumably by inactivation of the mRNA followed by its degradation. A model is proposed which involves selective inactivation of r-protein mRNA by a feedback mechanism. The model can explain coordinated synthesis of r-proteins and other observations related to selective expression of certain alleles in diploid strains.Ribosomes from Escherichia coli contain approximately 50 proteins. All of these proteins, with the exception of L7/L12, exist in a single copy per ribosome. In exponentially growing cells, there appears to be neither a significant pool of free ribosomal proteins (r-proteins) nor significant degradation of newly synthesized r-proteins. Therefore, all the r-proteins are apparently synthesized coordinately and stoichiometrically (for a review, see ref. 1). How this remarkable regulation is achieved is not known.In this paper, we report the results of experiments that show that E. coli cells have the ability to regulate the rate of r-protein synthesis regardless of the rate of transcription of r-protein genes. We then describe a new model which involves selective inactivation of r-protein mRNA by a feedback mechanism and discuss various available experimental observations. EXPERIMENTAL PROCEDURES Two E. coli K-12 strains were used. Both are lysogenic derivatives of strain N01230 (trkA401, kdpABC5, spCr, strr, fusr). One (NO1275) carries XtrkA transducing phage and XcI857S7 helper phage. The other (NO1328) carries Xspc2 transducing phage and the same helper phage. These strains and phages have been described (2, 3). All other experimental procedures are described in the figure and table legends. RESULTSWe initially asked whether an increase in the number of gene copies leads to an increase in the synthesis rate of corresponding r-proteins or if E. coli cells have the ability to regulate the synthesis rate regardless of gene copy numbers. The Xspc2 transducing phage carries 14 r-protein genes together with their promoters and 9 additional r-protein genes without their bacterial promoters (3, 4). The former 14 genes are organized into two operons ("...

The expression of the cloned tufB gene in vivo

“…It is of interest to note that the lack of gene dosage effect has been reported for the synthesis of ribosomal proteins [ 18-241 and of the /3 and 0' subunits of RNA polymerase [ 171. In some cases [20,21,231, it has been shown that the rate of transcription of mRNA increases as the number of the corresponding gene copies increases, yet no dosage effect was observed in the synthesis of the respective proteins. This suggests that expression of these genes may be regulated by post-transcriptional control, including the inactivation or degradation of mRNA.…”

“…This suggests that expression of these genes may be regulated by post-transcriptional control, including the inactivation or degradation of mRNA. This regulation was interpreted by a model in which free ribosomal proteins, when overproduced, selectively inactivate their own mRNA by a feedback mechanism [ 19,20,24]. It remains to be seen whether the similar regulatory mechanism may be present in the case of EF-Tu biosynthesis.…”

The structure of a ribosomal protein S8/spc operon mRNA complex

“…In the late 1970s, it was proposed that autoregulatory ribosomal proteins bind their own mRNAs the same way they bind to rRNA in the ribosome because their mRNAs and rRNAs have locally similar three-dimensional structure (Fallon et al 1979;Lindahl and Zengel 1979;Fiil et al 1980;Nomura et al 1980). This idea was attractive because if the RNA-binding activity that enables these proteins to participate in ribosome assembly also causes translational regulation, competition between rRNAs and ribosomal protein mRNAs will guarantee that the production of ribosomal proteins decreases when supply exceeds demand.…”

Regulation of human RPS14 transcription by intronic antisense RNAs and ribosomal protein S14.

“…Ribosomal protein (r-protein} gene expression is coordinated with cellular metabolism in bacteria through autoregulatory mechanisms that operate at the levels of transcription Skouv et al 1990;, mRNA processing (Fallon et al 1979;Mackie 1991), and protein biosynthesis Cole and Nomura 1986;Kearney and Nomura 1987;Thomas et al 1987;Mattheakis et al 1989;Portier et al 1990;Wikstr6m et al 1992). Yeast strains employ a similar set of control mechanisms to regulate r-protein gene expression during (Della Sita et al 1990;Mager andPlanta 1990, 1991;Moehle and Hinnebusch 1991;Presutti et al 1991;Papciak and Pearson 1992) and after (Gorenstein and Warner 1976;Kief and Warner 1981;Pearson et al 1982;Warner et al 1985;Dabeva and Warner 1993) transcription.…”