The 3072-nucleotide-long sequence of a segment from the 88-min region of the Escherichia coli chromosome has been determined. The sequence covers the genes for ribosomal proteins LIi (rpK), LI (rpMA), Li (rplJ, and L7/L12 (rpIL), and the 5' end of the gene for the /3 subunit of RNA polymerase (rpoB), along with the presumed regulatory regions for these genes. The probable locations of the promoter for the first two genes (the LII operon) and the promoter for the latter three genes (the proximal part of the /3 operon) have been identified. We have also found that the four ribosomal protein genes preferentially use codons that are recognized efficiently by the most abundant tRNA species. These and other features of the sequence results are discussed in relation to available information obtained from both in vitro and in vivo experiments on the expression of these ribosomal and RNA polymerase subunit genes.

Blood-group A and B isoantigens of sphingoglycolipid nature with a single carbohydrate chain have been isolated from human erythrocytes.

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 ("...

No abstract