Genetic studies of the ribosomal proteins in Escherichia coli. X. Mapping of the ribosomal proteins, L21 and S15, by intergeneric mating experiments between Serratia marcescens and Escherichia coli K12

Polynucleotide phosphorylase of Escherichia coli is required for the establishment of bacteriophage P4 immunity

Bacteriophage P4's superinfection immunity mechanism is unique among those of other known bacteriophages in several respects: (i) the P4 immunity factor is not a protein but a short, stable RNA (CI RNA); (ii) in the prophage the expression of the replication operon is prevented by premature transcription termination rather than by repression of transcription initiation; (iii) transcription termination is controlled via RNA-RNA interactions between the CI RNA and two complementary target sequences on the nascent transcript; and (iv) the CI RNA is produced by processing of the same transcript it controls. It was thought that several host-encoded factors may participate in the molecular events required for P4 immunity expression, i.e., RNA processing, RNA-RNA interactions, and transcription termination. To identify such factors we searched for Escherichia coli mutations that affect P4 lysogenization. One such mutation, bfl-1, severely reduced P4's lysogenization frequency and delayed both the disappearance of the long transcripts that cover the entire replication operon and the appearance of the CI RNA. By physical mapping and genetic analysis we show that bfl-1 is allelic to pnp, which codes for polynucleotide phosphorylase, a 3'-to-5' exonucleolytic enzyme. A previously isolated pnp null mutant (pnp-7) exhibited a phenotype similar to that of bfl-1. These results indicate that the polynucleotide phosphorylase of E. coli is involved with the maturation pathway of bacteriophage P4's RNA immunity factor.

Isolation of a Serratia marcescens mutant which is an efficient recipient for the E. coli episome

A Serratia marcescens mutant, which is an efficient recipient for the Escherichia coli episome (F' plasmid), was isolated after mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine (NTG). Episomes could be maintained in the mutant cell under conditions selective for a gene on the plasmid. This S. marcescens mutant could also be transformed with pBR 322 DNA at a frequency higher than that of the parental strain.

Protein synthesis defects in temperature-sensitive mutants of Escherichia coli with altered ribosomal proteins

The ribosomes from four temperature-sensitive mutants of Escherichia coli have been examined for defects in cell-free protein synthesis. The mutants examined had alterations in ribosomal proteins S10, S15, or L22 (two strains). Ribosomes from each mutant showed a reduced activity in the translation of phage MS2 RNA at 44 degrees C and were more rapidly inactivated by heating at this temperature compared to control ribosomes. Ribosomal subunits from three of the mutants demonstrated a partial or complete inability to reassociate at 44 degrees C. 70-S ribosomes from two strains showed a reducton in messenger RNA binding. tRNA binding to the 30 S subunit was reduced in the strains with altered 30-S proteins and binding to the 50 S subunit was affected in the mutants with a change in 50 S protein L22. The relation between ribosomal protein structure and function in protein synthesis in these mutants is discussed.

Mapping by interspecies transformation experiments of several ribosomal protein genes near the replication origin of Bacillus subtilis chromosome

Bacillus subtilis 168 was transformed with DNAs from B. amyloliquefaciens K or B. licheniformis IAM 11054. These two species show a considerable difference in ribosomal proteins from B. subtilis. Analyses of the transformants indicated that the genes for 16 proteins, S3, S5, S8, S12, S17, S19, BL1, BL5, BL6, BL8, BL14, BL16, BL17, BL22, BL23 and BL25 are located in the cysA-str-spc region on B. subtilis chromosome. The genes for 10 proteins, S4, S6, S13, S16, S20, BL15, BL18, BL20, BL24 and BL28 could not be found in this region in the present experiments.

Genetic studies of the ribosomal proteins in Escherichia coli. XI. Mapping of the genes for L21, L27, S15 and S21 by using hybrid bacteria and over-production of these proteins in the merodiploid strains

E. coli episomes which cover argG region were transferred to S. marcescens and ribosomal proteins (r-proteins) from these hybrid strains were analyzed by two-dimensional (2D) polyacrylamide gel electrophoresis. Three E. coli r-proteins L21, L27 and S15 could be detected in the ribosomes from the hybrid strains. The relative rate of synthesis of the individual r-proteins were determined for E. coli merodiploid strains harboring these episomes. Over-production of three r-proteins L21, L27 and S21 (but not S15) was observed in the merodiploid strains.

Synthesis of ribosomal proteins in merodiploid strains and in minicells of Escherichia coli

Merodiploid strains of Escherichia coli containing episomes which carry one or several of the ribosomal protein (r-protein) transcriptional units were analysed to see whether the increase in the number of gene copies leads to an increased synthesis of the respective r-proteins. It was found that the amount of ribosomal proteins was (with the only exception of ribosomal protein S20) independent of the number of gene copies present. The comparison of the in vivo stability of r-proteins in haploid and merodiploid strains did not, within the time resolution of the experiment, provide any evidence for an increased rate of degradation of those proteins coded by more than one gene copy. These results indicate a tight coupling between the amount of ribosomal proteins synthesized and the level required irrespective of the number of gene copies present. With the aid of minicells from a strain containing the episome F'101 which carries the thr-leu segment of the chromosome it was demonstrated that (i) in vivo synthesis of r-protein S20 could proceed in the absence of the synthesis of ribosomal RNA and of other r-proteins, and (ii) r-protein S20 was degraded under conditions where it was not assembled into ribosomes.

A new ribosomal protein locus in Escherichia coli: the gene for protein S6 maps at 97 min

A mutant of E. coli selected for temperature-sensitive growth on rich medium harbored an altered ribosomal protein S6 (Isono et al., 1976). This mutant was found to possess at least two mutations, one being responsible for the temperature-sensitivity and the other for the S6 alteration. Crosses with various Hfr strains as well as transductions with P 1kc revealed that the former mutation mapped at 98 min and the latter at 97 min. Furthermore, rec A derivatives of this mutant heteromerodiploid for this region possessed both the wild type and themutant forms of S6. Thus it was established that the gene at 97 min was indeed the structural gene for protein S6 (rpsF) and not a gene modifying it.

Genetic studies of the ribosomal proteins in Escherichia coli. X. Mapping of the ribosomal proteins, L21 and S15, by intergeneric mating experiments between Serratia marcescens and Escherichia coli K12

Episomes of E. coli, which cover argG but not the str region, were transferred to Serratia marcescens. Ribosomal proteins from these hybrid strains were analyzed with phospho-cellulose or carboxy-methyl-cellulose column chromatography. Two E. coli ribosomal proteins, L21 and S15, could be detected in the ribosome from the hybrid strains in addition to the ribosomal proteins of S. marcescens.