Abortive bacteriophage T4 head assembly in mutants of Escherichia coli

Structural and Functional Features of Viral Chaperonins

Chaperonins provide proper folding of proteins in vivo and in vitro and, as was thought until recently, are characteristic of prokaryotes, eukaryotes, and archaea. However, it turned out that some bacteria viruses (bacteriophages) encode their own chaperonins. This review presents results of the investigations of the first representatives of this new chaperonin group: the double-ring EL chaperonin and the single-ring OBP and AR9 chaperonins. Biochemical properties and structure of the phage chaperonins were compared within the group and with other known group I and group II chaperonins.

Chaperonin-assisted protein folding: a chronologue

This chronologue seeks to document the discovery and development of an understanding of oligomeric ring protein assemblies known as chaperonins that assist protein folding in the cell. It provides detail regarding genetic, physiologic, biochemical, and biophysical studies of these ATP-utilizing machines from both in vivo and in vitro observations. The chronologue is organized into various topics of physiology and mechanism, for each of which a chronologic order is generally followed. The text is liberally illustrated to provide firsthand inspection of the key pieces of experimental data that propelled this field. Because of the length and depth of this piece, the use of the outline as a guide for selected reading is encouraged, but it should also be of help in pursuing the text in direct order.

Novel chaperonins are prevalent in the virioplankton and demonstrate links to viral biology and ecology

Chaperonins are protein-folding machinery found in all cellular life. Chaperonin genes have been documented within a few viruses, yet, surprisingly, analysis of metagenome sequence data indicated that chaperonin-carrying viruses are common and geographically widespread in marine ecosystems. Also unexpected was the discovery of viral chaperonin sequences related to thermosome proteins of archaea, indicating the presence of virioplankton populations infecting marine archaeal hosts. Virioplankton large subunit chaperonin sequences (GroELs) were divergent from bacterial sequences, indicating that viruses have carried this gene over long evolutionary time. Analysis of viral metagenome contigs indicated that: the order of large and small subunit genes was linked to the phylogeny of GroEL; both lytic and temperate phages may carry group I chaperonin genes; and viruses carrying a GroEL gene likely have large double-stranded DNA (dsDNA) genomes (>70 kb). Given these connections, it is likely that chaperonins are critical to the biology and ecology of virioplankton populations that carry these genes. Moreover, these discoveries raise the intriguing possibility that viral chaperonins may more broadly alter the structure and function of viral and cellular proteins in infected host cells.

Molecular biology and biotechnology of bacteriophage

The development of the molecular biology of bacteriophage such as T4, lambda and filamentous phages was described and the process that the fundamental knowledge obtained in this field has subsequently led us to the technology of phage display was introduced.

The N Terminus of the Head Protein of T4 Bacteriophage Directs Proteins to the GroEL Chaperonin

The head protein of T4 bacteriophage requires the GroEL chaperonin for its insertion into a growing T4 head. Hundreds of thousands of copies of this protein must pass through the chaperonin in a limited time later in infection, indicating that the protein must use GroEL very efficiently and may contain sequences that bind tightly to GroEL. We show that green fluorescent protein (GFP) fused to the N terminus of the head protein can fold at temperatures higher than those at which the GFP protein can fold well by itself. We present evidence that this folding is promoted by the strong binding of N-terminal head protein sequences to GroEL. This binding is so strong that some fusion proteins can apparently deplete the cell of the GroEL needed for other cellular functions, altering the cellular membranes and slowing growth.

Deletion of a chaperonin 60 beta gene leads to cell death in the Arabidopsis lesion initiation 1 mutant

Lesion mimic mutants develop spontaneous cell death without pathogen attack. Some of the genes defined by these mutations may function as regulators of cell death, whereas others may perturb cellular metabolism in a way that leads to cell death. To understand the molecular mechanism of cell death in lesion mimic mutants, we isolated a lesion initiation 1 (len1) mutant by a T-DNA tagging method. The len1 mutant develops lesions on its leaves and expresses systemic acquired resistance (SAR). LEN1 was identified to encode a chloroplast chaperonin 60 beta (Cpn60 beta), a homologue of bacterial GroEL. The recombinant LEN1 had molecular chaperone activity for suppressing protein aggregation in vitro. Moreover, len1 plants develop accelerated cell death to heat shock stress in comparison with wild-type plants. The chlorophyll a/b binding protein (CAB) was present in len1 plants at a lower level than in the wild-type plants. These results indicate that LEN1 functions as a molecular chaperone in chloroplasts and its deletion leads to cell death in Arabidopsis.

Bacteriophage T4 genome

Phage T4 has provided countless contributions to the paradigms of genetics and biochemistry. Its complete genome sequence of 168,903 bp encodes about 300 gene products. T4 biology and its genomic sequence provide the best-understood model for modern functional genomics and proteomics. Variations on gene expression, including overlapping genes, internal translation initiation, spliced genes, translational bypassing, and RNA processing, alert us to the caveats of purely computational methods. The T4 transcriptional pattern reflects its dependence on the host RNA polymerase and the use of phage-encoded proteins that sequentially modify RNA polymerase; transcriptional activator proteins, a phage sigma factor, anti-sigma, and sigma decoy proteins also act to specify early, middle, and late promoter recognition. Posttranscriptional controls by T4 provide excellent systems for the study of RNA-dependent processes, particularly at the structural level. The redundancy of DNA replication and recombination systems of T4 reveals how phage and other genomes are stably replicated and repaired in different environments, providing insight into genome evolution and adaptations to new hosts and growth environments. Moreover, genomic sequence analysis has provided new insights into tail fiber variation, lysis, gene duplications, and membrane localization of proteins, while high-resolution structural determination of the "cell-puncturing device," combined with the three-dimensional image reconstruction of the baseplate, has revealed the mechanism of penetration during infection. Despite these advances, nearly 130 potential T4 genes remain uncharacterized. Current phage-sequencing initiatives are now revealing the similarities and differences among members of the T4 family, including those that infect bacteria other than Escherichia coli. T4 functional genomics will aid in the interpretation of these newly sequenced T4-related genomes and in broadening our understanding of the complex evolution and ecology of phages-the most abundant and among the most ancient biological entities on Earth.

Genetic analysis of bacteriophage-encoded cochaperonins

Early genetic studies identified the Escherichia coli groES and groEL genes because mutations in them blocked the growth of bacteriophages lambda and T4. Subsequent genetic and biochemical analyses have shown that GroES and GroEL constitute a chaperonin machine, absolutely essential for E. coli growth, because it is needed for the correct folding of many of its proteins. In spite of very little sequence identity to GroES, the bacteriophage T4-encoded Gp31 protein and the bacteriophage RB49-encoded CocO protein are bona fide GroEL cochaperonins, even capable of substituting for GroES in E. coli growth. A major functional distinction is that only Gp31 and CocO can assist GroEL in the correct folding of Gp23, the major bacteriophage capsid protein. Conserved structural features between CocO and Gp31, which are absent from GroES, highlight their potential importance in specific cochaperonin function.

Genetic analysis of the bacteriophage T4-encoded cochaperonin Gp31

Previous genetic and biochemical analyses have established that the bacteriophage T4-encoded Gp31 is a cochaperonin that interacts with Escherichia coli's GroEL to ensure the timely and accurate folding of Gp23, the bacteriophage-encoded major capsid protein. The heptameric Gp31 cochaperonin, like the E. coli GroES cochaperonin, interacts with GroEL primarily through its unstructured mobile loop segment. Upon binding to GroEL, the mobile loop adopts a structured, beta-hairpin turn. In this article, we present extensive genetic data that strongly substantiate and extend these biochemical studies. These studies begin with the isolation of mutations in gene 31 based on the ability to plaque on groEL44 mutant bacteria, whose mutant product interacts weakly with Gp31. Our genetic system is unique because it also allows for the direct selection of revertants of such gene 31 mutations, based on their ability to plaque on groEL515 mutant bacteria. Interestingly, all of these revertants are pseudorevertants because the original 31 mutation is maintained. In addition, we show that the classical tsA70 mutation in gene 31 changes a conserved hydrophobic residue in the mobile loop to a hydrophilic one. Pseudorevertants of tsA70, which enable growth at the restrictive temperatures, acquire the same mutation previously shown to allow plaque formation on groEL44 mutant bacteria. Our genetic analyses highlight the crucial importance of all three highly conserved hydrophobic residues of the mobile loop of Gp31 in the productive interaction with GroEL.

Substrate mutations that bypass a specific Cpn10 chaperonin requirement for protein folding

The bacteriophage T4 GroES homologue, gp31, in conjunction with the Escherichia coli chaperonin GroEL, is both necessary and sufficient to fold the T4 major capsid protein, gp23, to a state competent for capsid assembly as shown by in vivo expression studies. GroES is unable to function in this role as a productive co-chaperonin. The sequencing and characterization of mutations within gp23 that confer GroEL and gp31 chaperonin-independent folding of the mutant protein suggest that the chaperonin requirements are due to specific sequence determinants or structures in critical regions of gp23 that behave in an additive fashion to confer a chaperonin bypass phenotype. Conservative amino acid substitutions in these critical regions enable gp23 to fold in a GroEL-gp31 chaperonin-independent mode, albeit less efficiently than wild type, both in vivo and in vitro. Although the presence of functional GroEL-gp31 enhances folding of the mutated gp23 in vivo, GroEL-GroES has no such effect. Site-directed mutagenesis experiments suggest that a translational pausing mechanism is not responsible for the bypass mutant phenotype. Polyhead reassembly experiments are also consistent with direct, post-translational effects of the bypass mutations on polypeptide folding. Given our finding that gp31 is not required for the binding of the major capsid protein to GroEL and that active GroES is incapable of folding the gp23 polypeptide chain to native conformation, our results suggest co-chaperonin specificity in the folding of certain substrates.

ADP-ribosylation and early transcription regulation by bacteriophage T4

Bacteriophage T4 codes at least for two ADP-ribosylating activities, the 76 kDa Alt and the 24 kDa Mod gene products. The main target for both enzymes is the host RNA polymerase. We cloned and sequenced the alt gene and overexpressed the corresponding enzyme. The recombinant protein shows ADP-ribosylating activities in vitro, as had been described earlier for the native enzyme isolated from phage heads. The native as well as the recombinant protein ADP-ribosylate the alpha-subunit of RNA polymerase, but also subunits beta, beta' and sigma 70 and perform an autoribosylation reaction. Taking advantage of the pKWIII test system, constructed to measure promoter strengths in vivo, it was found that ADP-ribosylation of RNA polymerase leads to an increase of transcription from T4 early promoters up to a factor of two. In an infected host cell this should cause an enhanced expression of T4 genes. Depending on whether RNA polymerase was ADP-ribosylated or not, it initiated transcription at T4 promoters with different sequence characteristics: unribosylated RNA polymerase recognizes the early T4 promoters by an extended -10 region, whereas the ribosylated enzyme selects for T4 early promoters with an extended T4-specific and highly conserved -35 region. These results may reflect how the virus, step by step imposes its genetic program on the host cell, and in part they give a rationale for the extension of the consensus sequence observed with these promoters. We also sequenced the genomic region of the T4 mod gene and found two open reading frames coding both for proteins of approximately 24 kDa. Up to now none of the reading frames could be cloned into E. coli in an active form, making it highly probable that the ADP-ribosylation pattern inflicted by gene product Mod on host RNA polymerase is deleterious to these bacteria. Comparisons of the amino acid sequences showed significant homologies among the two reading frames. Computer analysis reveals that both Mod sequences and also the sequence of the Alt protein exhibit a structural concordance with the catalytic domains of other prokaryotic ADP-mono-ribosyltransferases such as the Pseudomonas aeruginosa exotoxin A, the cholera labile enterotoxin, the diphteria toxin, the heat labile enterotoxin A of E. coli, and pertussis toxin. We present a detailed model for T4 transcription regulation.

Molecular chaperones in cellular protein folding

The folding of many newly synthesized proteins in the cell depends on a set of conserved proteins known as molecular chaperones. These prevent the formation of misfolded protein structures, both under normal conditions and when cells are exposed to stresses such as high temperature. Significant progress has been made in the understanding of the ATP-dependent mechanisms used by the Hsp70 and chaperonin families of molecular chaperones, which can cooperate to assist in folding new polypeptide chains.

Stability of wild-type and temperature-sensitive protein subunits of the phage P22 capsid

Temperature-sensitive folding (tsf) mutants of the phage P22 coat protein prevent newly synthesized polypeptide chains from reaching the conformation competent for capsid assembly in cells, and can be rescued by the GroEL chaperone (Gordon, C., Sather, S., Casjens, S., and King, J. (1994) J. Biol. Chem. 269, 27941-27951). Here we investigate the stabilities of wild-type and four tsf mutant unpolymerized subunits. Wild-type coat protein subunits denatured at 40 degrees C, with a calorimetric enthalpy of approximately 600 kJ/mol. Comparison with coat protein denaturation within the shell lattice (Tm = 87 degrees C, delta H approximately 1700 kJ/mol) (Galisteo, M.L., and King, J. (1993) Biophys. J. 65, 227-235) indicates that protein-protein interactions within the capsid provide enormous stabilization. The melting temperatures of the subunits carrying tsf substitutions were similar to wild-type. At low temperatures, the tsf mutants, but not the wild-type, formed non-covalent dimers, which were dissociated at temperatures above 30 degrees C. Spectroscopic and calorimetric studies indicated that the mutant proteins have reduced amounts of ordered structure at low temperature, as compared to the wild-type protein. Although complex, the in vitro phenotypes are consistent with the in vivo finding that the mutants are defective in folding, rather than subunit stability. These results suggest a role for incompletely folded subunits as precursors in viral capsid assembly, providing a mechanism of reaching multiple conformations in the polymerized form.

Two classes of extragenic suppressor mutations identify functionally distinct regions of the GroEL chaperone of Escherichia coli

The GroES and GroEL proteins of Escherichia coli function together as the GroE molecular chaperone machine to (i) prevent denaturation and aggregation and (ii) assist the folding and oligomerization of other proteins without being part of the final structure. Previous genetic and biochemical analyses have determined that this activity requires interactions of the GroES 7-mer with the GroEL 14-mer. Recently, we have identified a region of the GroES protein that interacts with the GroEL protein. To identify those residues of the GroEL protein that interact with GroES, we have exploited the thermosensitive phenotype of strains bearing mutations at one or the other of two GroEL-interacting residues of GroES. We have isolated, cloned, and sequenced six suppressor mutations in groEL, three independent isolates for each groES mutant. Changes of only three different amino acid substitutions in GroEL protein were found among these six groEL suppressor mutations. On the basis of a number of in vivo analyses of the chaperone activity of various combinations of groES mutant alleles and groEL suppressor alleles, we propose that an amino-proximal region of the GroEL protein which includes amino acid residues 174 and 190 interacts with GroES and that a carboxyl-proximal region which includes residue 375 interacts with substrate proteins.

A carboxy-terminal deletion impairs the assembly of GroEL and confers a pleiotropic phenotype in Escherichia coli K-12

A series of COOH-terminal deletions of the chaperonin GroEL have been examined for effects in vivo at haploid copy number on the essential requirement of GroEL for cell growth. Strains with a deletion of up to 27 COOH-terminal amino acids were viable, but not viable strain could be isolated with a deletion of 28 or more codons. When substitutions were placed in the COOH-terminal amino acid Val-521 of the 27-amino-acid-deleted (delta 27) mutant, we found variable effect--Trp and Glu led to inviability, whereas Arg and Gly were viable but slow growing. The effects of the Arg substitution plus deletion (V521R delta) were examined in more detail. Whereas the delta 27 mutant with the wild-type residue Val-521 grew as well as a strain with wild-type GroEL, the V521R delta mutant strain (groEL202) exhibited a broad range of phenotypic defects. These include slow growth; filamentous morphology; a defect in plating lambda; absence of activity of expressed human ornithine transcarbamylase, as seen in other GroEL mutants; and several newly observed defects, such as absence of motility, sensitivity to UV light and mitomycin, a defect in one mode of specialized transduction, and inability to grow on rhamnose. Sucrose gradient analysis of extracts from the V521R delta cells showed a substantially reduced level of GroEL sedimenting at the normal 20S position of the assembled tetradecamer and a relatively large amount of more lightly sedimenting subunits. This indicates that the substitution-deletion mutation interferes with oligomeric assembly of GroEL into its functional form. This is discussed in light of the recently determined crystal structure of GroEL.

A eukaryotic cytosolic chaperonin is associated with a high molecular weight intermediate in the assembly of hepatitis B virus capsid, a multimeric particle

We have established a system for assembly of hepatitis B virus capsid, a homomultimer of the viral core polypeptide, using cell-free transcription-linked translation. The mature particles that are produced are indistinguishable from authentic viral capsids by four criteria: velocity sedimentation, buoyant density, protease resistance, and electron microscopic appearance. Production of unassembled core polypeptides can be uncoupled from production of capsid particles by decreasing core mRNA concentration. Addition of excess unlabeled core polypeptides allows the chase of the unassembled polypeptides into mature capsids. Using this cell-free system, we demonstrate that assembly of capsids proceeds by way of a novel high molecular weight intermediate. Upon isolation, the high molecular weight intermediate is productive of mature capsids when energy substrates are manipulated. A 60-kD protein related to the chaperonin t-complex polypeptide 1 (TCP-1) is found in association with core polypeptides in two different assembly intermediates, but is not associated with either the initial unassembled polypeptides or with the final mature capsid product. These findings implicate TCP-1 or a related chaperonin in viral assembly and raise the possibility that eukaryotic cytosolic chaperonins may play a distinctive role in multimer assembly apart from their involvement in assisting monomer folding.

Sequence analysis and phenotypic characterization of groEL mutations that block lambda and T4 bacteriophage growth

The groES and groEL genes of Escherichia coli have been shown previously to belong to a single operon under heat shock regulation. Both proteins have been universally conserved in nature, as judged by the presence of similar proteins throughout evolution. The GroEL protein has been shown to bind promiscuously to many unfolded proteins, thus preventing their aggregation. ATP hydrolysis by GroEL results in the release of the bound polypeptides, a process that often requires the action of GroES. In an effort to understand GroEL and GroES structure and function, we have determined the nucleotide changes of nine mutant alleles of groEL. All of these mutant alleles were isolated because they block bacteriophage lambda growth. Our sequencing results demonstrate that (i) many of these alleles are identical, in spite of the fact that they were independently isolated, and (ii) most of the different alleles are clustered in the same region of the gene. One of the mutant alleles was shown to possess two nucleotide alterations in the groEL coding phase, one of which is located in a putative ATP-binding domain. The two nucleotide changes were separated by genetic engineering, and each individual change was shown to exert an effect on bacteriophage growth. But, using genetic analyses, we demonstrate that the restriction on bacterial growth at elevated temperatures is conferred only by the mutation within the putative ATP-binding domain. We have cloned the mutant alleles on multicopy plasmids and overexpressed their products. By testing for the ability of bacteriophage either to propagate or to form colonies at 43 degrees C, we have been able to divide the mutant proteins into those with no activity and those with residual activity under the various conditions tested.

Response of mammalian cells to metabolic stress; changes in cell physiology and structure/function of stress proteins

In response to adverse changes in their local environment, cells or tissues from all organisms increase the expression of a group of proteins referred to as heat shock or stress proteins. Collectively, the stress proteins are thought to provide the cell with some degree of protection during the environmental insult as well as facilitate the repair and recovery of metabolic pathways perturbed as a consequence of the stress event. Within the past few years it has become apparent that most all of the stress proteins are present in appreciable levels in the unstressed cell and are involved in a number of very basic and essential biochemical pathways. The present review has discussed pertinent changes in cell physiology in mammalian cells experiencing metabolic stress. In addition, considerable attention has been given to discussing the properties and possible functions of the individual stress proteins.

Mutational analysis of the phage T4 morphogenetic 31 gene, whose product interacts with the Escherichia coli GroEL protein

The phage T4 morphogenetic gene 31 has been sequenced. Its deduced gene product is a polypeptide of 111 aa, with a predicted Mr of 12064 and a pI of 4.88. The proof that the assigned open reading frame (ORF) encodes Gp31 rests on the sequencing of two known gene 31 amber mutations, amN54 and NG71, demonstrating that these mutations result in translational termination within the assigned ORF. Furthermore, the sequencing of four different T4 epsilon mutations, isolated on the basis of allowing the phage to propagate on Escherichia coli groEL- hosts, showed that they are either missense mutations or 3-bp deletions in the gene 31 reading frame. The sequencing of neighboring DNA revealed the presence of five other ORFs, one of which overlaps gene 31 substantially, but in the opposite orientation.

Polypeptide chain binding proteins: catalysts of protein folding and related processes in cells

Subcellular compartments in which folding and assembly of proteins occur seem to have a set of PCB proteins capable of mediating these and related processes, such as translocation across membranes. When a domain of a polypeptide chain emerges from a ribosome during synthesis or from the distal side of a membrane during translocation, successive segments of the chain are incrementally exposed to solvent and yet are unlikely to be able to fold. This topological restriction on folding likely mandates a need for PCB proteins to prevent aggregation. Catalysis of topologically restricted folding by PCB proteins is likely to involve both an antifolding activity that postpones folding until entire domains are available and, more speculatively, a folding activity resulting from a programmed stepwise release that employs the energy of ATP hydrolysis to ensure a favorable pathway. We are left with a new set of problems. How do proteins fold in cells? What are the sequences or structural signals that dictate folding pathways? The new challenge will be to understand folding as a combination of physical chemistry, enzymology, and cell biology.

Peptide binding and release by proteins implicated as catalysts of protein assembly

Two members of the hsp70 family, termed hsc70 and BiP, have been implicated in promoting protein folding and assembly processes in the cytoplasm and the lumen of the endoplasmic reticulum, respectively. Short hydrophilic (8 to 25 residues) synthetic peptides have now been tested as possible mimics of polypeptide chain substrates to help define an enzymatic basis for these activities. Both BiP and hsc70 have specific peptide binding sites. Peptide binding elicits hydrolysis of adenosine triphosphate, with the subsequent release of bound peptide.

Identification and metabolic characterization of the Zea mays mitochondrial homolog of the Escherichia coli groEL protein

We have characterized an abundant mitochondrial protein from Zea mays and have shown it to be structurally and metabolically indistinguishable from a previously described Tetrahymena thermophila and Saccharomyces cerevisiae mitochondrial protein, referred to as hsp60, which is homologous to the groEL protein of Escherichia coli. This Z. mays protein, which we also refer to as hsp60, was found to be antigenically quite distinct from the chloroplast Rubisco-binding protein, another groEL homolog. Using an antiserum directed against the T. thermophila hsp60, we determined that the relative concentration of Z. mays hsp60 was two to four times higher in mitochondria isolated from tissues of early developmental stages than that found in mitochondria isolated from more adult tissues. Given the known and suggested roles of the other members of the groEL family of proteins, our results suggest that the Z. mays hsp60 may play an important role in mitochondrial biogenesis during early plant development.

Cloning, sequence, and expression of the temperature-dependent phage T4 capsid assembly gene 31

The products of the bacteriophage T4 capsid assembly gene 31, the T4 major capsid protein gene 23, and the Escherichia coli heat-shock groE genes participate in an interdependent mechanism in capsid protein oligomerization early in prohead assembly. Gene 31 was cloned, sequenced and expressed, and its regulation during infection was characterized. Gene 31 is more stringently required at high than at low temperature, and this requirement is reduced by temperature adaptation of the bacteria prior to infection. However, T4 gene 31 expression does not appear to be temperature regulated, nor does gene 31 apparently display sequence homology with the E. coli groE and other heat-shock genes.

Homologous plant and bacterial proteins chaperone oligomeric protein assembly

An abundant chloroplast protein is implicated in the assembly of the oligomeric enzyme ribulose bisphosphate carboxylase-oxygenase, which catalyses photosynthetic CO2-fixation in higher plants. The product of the Escherichia coli groEL gene is essential for cell viability and is required for the assembly of bacteriophage capsids. Sequencing of the groEL gene and the complementary cDNA encoding the chloroplast protein has revealed that these proteins are evolutionary homologues which we term 'chaperonins'. Chaperonins comprise a class of molecular chaperones that are found in chloroplasts, mitochondria and prokaryotes. Assisted post-translational assembly of oligomeric protein structures is emerging as a general cellular phenomenon.

Control of cell division by sex factor F in Escherichia coli. III. Participation of the groES (mopB) gene of the host bacteria

Cell division of F+ bacteria is coupled to DNA replication of the F plasmid. Two plasmid coded genes, letA (ccdA) and letD (ccdB) are indispensable for this coupling. To investigate bacterial genes that participate in this coupling, we attempted to identify the target of the division inhibitor (the letD gene product) of the F plasmid. Two temperature-sensitive growth defective mutants were screened from bacterial mutants that escaped the letD product growth inhibition that occurs in hosts carrying an FletA mutant. Phage P1-mediated transduction and complementation analysis indicated that the temperature-sensitive mutations are located in the groES (mopB) gene, which is essential for the morphogenesis of several bacteriophages and also for growth of the bacteria. The nucleotide sequence of the promoter region of the gene in which the temperature-sensitive mutations had occurred was virtually identical with that of the groES gene of Escherichia coli; furthermore the sequence of the first five amino acid residues and the overall amino acid composition predicted from the nucleotide sequence of the gene match those of the purified GroES protein. The temperature-sensitive mutants did not allow the propagation of phage lambda at 28 degrees C and formed long filamentous structures without septa at 41 degrees C, as is observed in the case of groES mutants. Growth of the two groES mutants tested was not inhibited by the F plasmid with the letA mutation. These observations suggest to us that the morphogenesis gene groES plays a key role in coupling between replication of the F plasmid and cell division of the host cells.

A highly evolutionarily conserved mitochondrial protein is structurally related to the protein encoded by the Escherichia coli groEL gene

We recently reported that a Tetrahymena thermophila 58-kilodalton (kDa) mitochondrial protein (hsp58) was selectively synthesized during heat shock. In this study, we show that hsp58 displayed antigenic similarity with mitochondrially associated proteins from Saccharomyces cerevisiae (64 kDa), Xenopus laevis (60 kDa), Zea mays (62 kDa), and human cells (59 kDa). Furthermore, a 58-kDa protein from Escherichia coli also exhibited antigenic cross-reactivity to an antiserum directed against the T. thermophila mitochondrial protein. The proteins from S. cerevisiae and E. coli antigenically related to hsp58 were studied in detail and found to share several other characteristics with hsp58, including heat inducibility and the property of associating into distinct oligomeric complexes. The T. thermophila, S. cerevisiae, and E. coli macromolecular complexes containing these related proteins had similar sedimentation characteristics and virtually identical morphologies as seen with the electron microscope. The distinctive properties of the E. coli homolog to T. thermophila hsp58 indicate that it is most likely the product of the groEL gene.

A highly evolutionarily conserved mitochondrial protein is structurally related to the protein encoded by the Escherichia coli groEL gene

We recently reported that a Tetrahymena thermophila 58-kilodalton (kDa) mitochondrial protein (hsp58) was selectively synthesized during heat shock. In this study, we show that hsp58 displayed antigenic similarity with mitochondrially associated proteins from Saccharomyces cerevisiae (64 kDa), Xenopus laevis (60 kDa), Zea mays (62 kDa), and human cells (59 kDa). Furthermore, a 58-kDa protein from Escherichia coli also exhibited antigenic cross-reactivity to an antiserum directed against the T. thermophila mitochondrial protein. The proteins from S. cerevisiae and E. coli antigenically related to hsp58 were studied in detail and found to share several other characteristics with hsp58, including heat inducibility and the property of associating into distinct oligomeric complexes. The T. thermophila, S. cerevisiae, and E. coli macromolecular complexes containing these related proteins had similar sedimentation characteristics and virtually identical morphologies as seen with the electron microscope. The distinctive properties of the E. coli homolog to T. thermophila hsp58 indicate that it is most likely the product of the groEL gene.

The bacteriophage T4 dexA gene: sequence and analysis of a gene conditionally required for DNA replication

We have cloned and sequenced a bacteriophage T4 EcoRI fragment that complements T4 del (39-56) infections of an optA defective Escherichia coli strain. Bacteria containing this recombinant plasmid synthesize two new proteins with molecular weights of 9 and 26 kilodaltons. We have identified the gene encoding the 26 kilodalton protein as essential for T4 infections of optA defective E. coli. Genetic and biochemical results are consistent with the identification of this protein as the product of the dexA gene, which encodes a 3' to 5' exonuclease.

Intracellular morphogenesis of bacteriophage T4. II. Head morphogenesis

The relative phage yields of cells of Escherichia coli infected with both wild-type and amber mutant phages deficient in head morphogenesis were determined. The decrease in burst size as a function of the ratio of mutant:wild-type-infecting phage was linear and proportional for mutants in genes 20, 22, and 23, while for mutants in genes 21, 31, and 24 the results suggest an excess of intracellular gene product. The initiation of assembly of phage particles was not delayed at reduced gene product levels; only a reduction in the rate of phage assembly was observed. The effects on burst size of pairs of mutations in genes 20 and 23, 22 and 23, and 22 and 24, in both cis and trans arrangements, were identical. Experiments using the mutant E920g in gene 23 show that varying the kind and intracellular amounts of the major capsid protein (gp23) with respect to the major core or scaffold protein (gp22) had a profound effect on the length of the T4 head. Head length determination must therefore depend on the proper intracellular balance between these two proteins.

Bacteriophage T4 bypass31 mutations that make gene 31 nonessential for bacteriophage T4 replication: isolation and characterization

T4 bacteriophage mutants called bypass31 (byp31) that specifically suppress gene 31 amber mutations have been isolated and characterized. The mechanism by which the byp31 mutation, byp31-1, suppresses gene 31 nonsense mutations does not involve synthesis of gp31 or of a particular gp31 fragment; furthermore, the byp31 allele suppresses all nonsense mutations in gene 31 that have been tested. We detect no unusual properties among the T4 particles made in su- cells by the T4amN54byp31-1 double mutant. These virions, made in the absence of gp31, show normal heat sensitivity, normal sensitivity to osmotic shock, and normal morphology. Specific different gene 31 missense mutants are able to form plaques with high efficiencies on the following two types of host defective cells: (i) Escherichia coli groEL (Tilly et al., Proc. Natl. Acad. Sci. U.S.A. 78:1629-1633, 1981) mutants that block T4 capsid assembly and (ii) E. coli rho mutants in which T4+ heads are assembled, but in which tail production and DNA synthesis are blocked. (Note that not all rho mutants block T4 production [G. Binkowski and L. D. Simon, p. 342-350, in C. K. Mathews, E. M. Kutter, G. Mosig, and P. B. Berget, ed., Bacteriophage T4, 1983]; T4 is able to replicate in rho mutants such as rho ts15, whose principal defect is that they fail to terminate transcription.) The byp31-1 allele permits production of T4 particles in E. coli groEL host-defective mutants, but not in E. coli rho host mutants.

Participation of Escherichia coli K-12 groE gene products in the synthesis of cellular DNA and RNA

Cells having the temperature-sensitive mutation groES131(Ts) were isolated from Escherichia coli K-12 strain C600T by thymineless death selection at 44 degrees C. This conditionally expressed mutation affected both cellular DNA and RNA syntheses at nonpermissive temperature, in addition to rendering cells unable to propagate phage lambda at permissive temperature.

Participation of the host protein(s) in the morphogenesis of bacteriophage P22

Spontaneous mutants of S. typhimurium resistant to thiolutin are conditionally non-permissive for phage P22 development (Joshi and Chakravorty 1979). At 40 degree C non-infective phage particles are produced. Phage development in two nonpermissive hosts (18/MC4 and 153/MC4) has been studied in detail. The steps at which the phage morphogenesis is interfered with differ in the two mutants. The electron micrograph of the particles produced in the mutant 18/MC4 reveals the presence of normal-looking particles; these particles contain phage DNA, adsorb to the permissive host but fail to inject their DNA. The particles produced in the mutant 153/MC4 which fail to adsorb to the host are found to be tail fibre-less. These observations indicate the involvement of host protein(s) in phage P22 morphogenesis.

Effect of bacteriophage lambda infection on synthesis of groE protein and other Escherichia coli proteins

We used two-dimensional gel electrophoresis to quantitate the changes in rates of synthesis that follow phage lambda infection for 21 Escherichia coli proteins, including groE and dnaK proteins. Although total protein synthesis and the rates of synthesis of most individual E. coli proteins decreased after infection, some proteins, including groE protein, dnaK protein, and stringent starvation protein, showed increases to rates substantially above their preinfection rates. Infection by lambda Q- affected host synthesis in the same way as infection by gamma+, whereas infection by lambda N- showed no detectable effect on host synthesis. Deletion of the early genes between att and N abolished the effect, and shorter deletions in this region gave intermediate effects. By this sort of deletion mapping, we show that a large part, though not all, of the effect of lambda infection on host protein synthesis can be ascribed to the early region that contains phage genes Ea10 and ral. We compared the changes in protein synthesis after infection with the changes that occur in uninfected cells upon heat shock or amino acid starvation. The spectrum of changes that occurred on infection was very different from that seen after heat shock but quite similar to that seen during amino acid starvation. Despite this similarity of the effects of lambda infection and starvation, we did not detect any increase in the level of guanosine tetraphosphate during infection. We show that the groE protein is the same protein as B56.5 of Lemaux et al. (Cell 13:427-434, 1978) and A protein of Subramanian et al. (Eur. J. Biochem. 67:591-601, 1976).

Identification of a second Escherichia coli groE gene whose product is necessary for bacteriophage morphogenesis

Previous work has uncovered the existence of an Escherichia coli locus, groE, that is essential for bacterial growth, lambda phage and T4 phage head morphogenesis, and T5 phage tail assembly. Our genetic and biochemical analyses of lambda groE+ transducing phages and their deletion and point mutant derivatives show that the groE locus consists of two closely linked genes. One groE gene, groEL, has been shown to encode the synthesis of a 65,000 Mr polypeptide, whereas the second, groES, codes for the synthesis of a 15,000 Mr polypeptide. About half of the groE- bacterial isolates fall into the groES complementation group. GroE mutations in either gene cause similar phenotypes, with respect to lambda phage head morphogenesis and bacterial growth at nonpermissive temperatures.

Identity of the B56.5 protein, the A-protein, and the groE gene product of Escherichia coli

Protein B56.5 is a major Escherichia coli protein, originally identified on two-dimensional gels as an abundant cellular protein with unique regulation. The groE gene product is a bacterial protein essential for the assembly of many diverse bacteriophages. The ribosomal A-protein is a large, acidic protein of unknown function associated with isolated, washed ribosomes. On the basis of comigration in two-dimensional gels, oligopeptide map patterns, amino acid composition, immunological specificity, physical properties, and genetic analysis, protein B56.5 has now been shown to be the groE gene product and to be identical with the A-protein.

Role of the host cell in bacteriophage T4 development. II. Characterization of host mutants that have pleiotropic effects on T4 growth

Mutant host-defective Escherichi coli that fail to propagate bacteriophage T4 and have a pleiotropic effect on T4 development have been isolated and characterized. In phage-infected mutant cells, specific early phage proteins are absent or reduced in amount, phage DNA synthesis is depressed by about 50%, specific structural phage proteins, including some tail and collar components, are deficient or missing, and host-cell lysis is delayed and slow. Almost all phage that can overcome the host block carry mutantions that map in functionally undefined 'nonessential' regions of the T4 genome, most near gene 39. The mutant host strains are temperature sensitive for growth and show simultaneous reversion of the ts phenotype and the inability to propagate T4+. The host mutations are cotransduced with ilv (83 min) and may lie in the gene for transcription termination factor rho.

Role of the host cell in bacteriophage T4 development. I. Characterization of host mutants that block T4 head assembly

To study the role of the host cell in bacteriophage T4 infection, we selected more than 600 mutant host-defective bacteria that absorbed and were killed by phage T4+ but were unable to support its growth. The mutants were grouped into seven classes by the growth patterns of T4 phages carrying compensating mutations (go mutants [grows on]), selected on four prototype host-defective strains. Lysis and DNA synthesis experiments indicated that classes A, AD, D, and B (the majority of the host-defective mutants) block T4+ development at an assembly step, class C mutants affect an early stage in phage development, and class F mutants appear to act at more than one stage. Analysis of T4+ infection in the assembly-defective mutants by in vitro complementation, electron microscopy, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the host-defective mutations interfere with T4+ capsid formation at the level of phage gene 31 function, before assembly of any recognizable capsid structure. The mutations map near purA, but at two or possibly three different sites. The go mutant phages able to overcome the host defect carry mutations in either gene 31, as found by others for similar defective hosts, or in the gene for the major capsid protein (gene 23). The gene 23 go mutations do not bypass the requirement for gene 31 function. These results suggest that at least three components must interact to initiate T4 head assembly: gp31, gp23, and one or more host factors. The compensatory effects of mutational alterations in these components are highly allele specific, consistent with the view that phage and host components interact directly in protein complexes.