Transcription of Ti plasmid-derived sequences in three octopine-type crown gall tumor lines

The type IV secretion protein TraK from the Enterococcus conjugative plasmid pIP501 exhibits a novel fold

Conjugative plasmid transfer presents a serious threat to human health as the most important means of spreading antibiotic resistance and virulence genes among bacteria. The required direct cell-cell contact is established by a multi-protein complex, the conjugative type IV secretion system (T4SS). The conjugative core complex spans the cellular envelope and serves as a channel for macromolecular secretion. T4SSs of Gram-negative (G-) origin have been studied in great detail. In contrast, T4SSs of Gram-positive (G+) bacteria have only received little attention thus far, despite the medical relevance of numerous G+ pathogens (e.g. enterococci, staphylococci and streptococci). This study provides structural information on the type IV secretion (T4S) protein TraK of the G+ broad host range Enterococcus conjugative plasmid pIP501. The crystal structure of the N-terminally truncated construct TraKΔ was determined to 3.0 Å resolution and exhibits a novel fold. Immunolocalization demonstrated that the protein localizes to the cell wall facing towards the cell exterior, but does not exhibit surface accessibility. Circular dichroism, dynamic light scattering and size-exclusion chromatography confirmed the protein to be a monomer. With the exception of proteins from closely related T4SSs, no significant sequence or structural relatives were found. This observation marks the protein as a very exclusive, specialized member of the pIP501 T4SS.

Genome-wide association studies and the clinic: a focus on breast cancer

Breast cancer is the most frequently diagnosed cancer among women worldwide, and has long been considered to be a genetic disease. A wide range of genetic variants, both rare mutations and more common variants, have been shown to influence breast cancer risk. In particular, recent studies have identified a number of common genetic variants, or single nucleotide polymorphisms, that are associated with breast cancer risk. In this review, we will briefly present the genetic epidemiology of breast cancer, genome-wide association study technology and how this technology may influence breast cancer screening in the clinic.

The 2.5 Å structure of the enterococcus conjugation protein TraM resembles VirB8 type IV secretion proteins

Conjugative plasmid transfer is the most important means of spreading antibiotic resistance and virulence genes among bacteria and therefore presents a serious threat to human health. The process requires direct cell-cell contact made possible by a multiprotein complex that spans cellular membranes and serves as a channel for macromolecular secretion. Thus far, well studied conjugative type IV secretion systems (T4SS) are of Gram-negative (G-) origin. Although many medically relevant pathogens (e.g., enterococci, staphylococci, and streptococci) are Gram-positive (G+), their conjugation systems have received little attention. This study provides structural information for the transfer protein TraM of the G+ broad host range Enterococcus conjugative plasmid pIP501. Immunolocalization demonstrated that the protein localizes to the cell wall. We then used opsonophagocytosis as a novel tool to verify that TraM was exposed on the cell surface. In these assays, antibodies generated to TraM recruited macrophages and enabled killing of pIP501 harboring Enteroccocus faecalis cells. The crystal structure of the C-terminal, surface-exposed domain of TraM was determined to 2.5 Å resolution. The structure, molecular dynamics, and cross-linking studies indicated that a TraM trimer acts as the biological unit. Despite the absence of sequence-based similarity, TraM unexpectedly displayed a fold similar to the T4SS VirB8 proteins from Agrobacterium tumefaciens and Brucella suis (G-) and to the transfer protein TcpC from Clostridium perfringens plasmid pCW3 (G+). Based on the alignments of secondary structure elements of VirB8-like proteins from mobile genetic elements and chromosomally encoded T4SS from G+ and G- bacteria, we propose a new classification scheme of VirB8-like proteins.

Recombination between higher plant DNA and the Ti plasmid of Agrobacterium tumefaciens

The Ti plasmid sequences (T-DNA) from the octopine-producing crown gall tumor A6S/2 were isolated by molecular cloning, using the bacteriophage lambda vector Charon 4A. Analysis of the cloned DNA segments indicates that the Ti plasmid sequences are covalently joined to plant nuclear DNA. These data demonstrate that genetic recombination between a eukaryote and a prokaryote can occur as a natural phenomenon.

Proteins encoded by Agrobacterium tumefaciens Ti plasmid DNA (T-DNA) in crown gall tumors

In order to detect proteins that may be produced in crown gall tumors as a result of expression of incorporated Agrobacterium tumefaciens Ti plasmid DNA (T-DNA), we have isolated mRNA complementary to T-DNA and translated this in a protein-synthesizing system derived from wheat germ. mRNA prepared from cultured E1 tumor from Nicotiana tabacum hybridized with HindIII fragment 1 sequences of T-DNA immobilized on cellulose nitrate filters. Two proteins of 30,000 and 16,500 M(r) were produced when this selected RNA was released and translated. Other tumor lines from N. tabacum were investigated, and a protein of slightly less than 30,000 M(r) was encoded by HindIII fragment 1 sequences of 15955/01 tumor. No products were observed for 15955/1 tumor line, which differs from E1/B6-806 and 15955/01 in that it does not produce octopine. mRNA species of each of the tumor lines hybridized to Bst I fragment 8 sequences of T-DNA and produced a common protein of 15,000 M(r). Because this protein is derived from the region of the T-DNA that is conserved in octopine- and nopaline-type crown gall tumors, it may play a role in oncogenicity.

Short direct repeats flank the T-DNA on a nopaline Ti plasmid

Crown gall disease results from the insertion of a segment of the Agrobacterium Ti plasmid, called T-DNA, into host plant nuclear DNA. We have subjected to sequence analysis the border regions of pTi T37 (ends of T-DNA) and one left T-DNA/plant DNA border fragment isolated from BT37 tobacco teratoma by molecular cloning. These sequence studies, taken together with published sequence of a right T-DNA/plant DNA border fragment, allowed us to identify the positions of left and right borders at the DNA sequence level. Comparison of left and right border regions of the Ti plasmid revealed a "core" direct repeat of 13 of 14 bases (12 contiguous) precisely at the borders of T-DNA. An extended repeat of 21 of 25 bases overlaps this core repeat. T-DNA on the Ti plasmid exhibits no longer direct or inverted repeats in the border regions, based on Southern hybridization studies. The physical structure of T-DNA differs from that of known prokaryotic and eukaryotic transposable elements but bears a structural resemblance to the prophage of bacteriophage lambda.

Agropine in "null-type" crown gall tumors: Evidence for generality of the opine concept

Agrobacterium Ti (tumor-inducing) plasmids, the causative agents of crown gall disease, fall into four genetic groups based on the patterns of octopine and nopaline synthesis (by crown gall tumors) and catabolism (by Agrobacterium tumefaciens) for which they are responsible. Two classes of Ti plasmids induce tumors that synthesize neither octopine nor nopaline. The existence of these Ti plasmids challenged the view that opines such as octopine and nopaline play a central role in crown gall biology. We now report the occurrence of an opine in tumors induced by one of these classes of Ti plasmids, the "null-type" plasmids typified by pTi Bo542. The opine was purified by biological enrichment based on its utilization by bacteria containing pTi Bo542 but not by bacteria lacking a Ti plasmid. The mass spectrum and biological properties of this opine are identical to those of agropine, an opine recently discovered in octopine-type tumors. We propose that null-type Ti plasmids now be named for their signal opine, agropine-type Ti plasmids.

T-DNA from Agrobacterium Ti plasmid is in the nuclear DNA fraction of crown gall tumor cells

The crown gall teratoma tumor line BT37, incited by Agrobacterium tumefaciens strain T37, has been found to contain part of the tumor-inducing plasmid, pTi T37, of the inciting strain. This foreign DNA segment, called T-DNA, is maintained at several copies per diploid tumor cell. We have examined subcellular DNA fractions from this tumor line in an effort to determine whether T-DNA is in chloroplasts, mitochondria, or nuclei. Tumor cell chloroplast DNA exhibited EcoRI and Bst I endonuclease cleavage patterns identical to those of normal tobacco chloroplast DNA. Tumor cell mitochondrial DNA exhibited a complex Bst I cleavage pattern that did not differ detectably from that of normal tobacco mitochondrial DNA. Southern blots of tumor chloroplast and mitochondrial cleavage products did not hybridize with labeled pTi T37 DNA, whereas blots of tumor cell nuclear DNA cleavage products hybridized strongly. We conclude that T-DNA is located not in chloroplasts or mitochondria but rather in the nuclear fraction of this tumor line.

Revertant seedlings from crown gall tumors retain a portion of the bacterial Ti plasmid DNA sequences

BT37 is a crown gall teratoma incited on tobacco by Agrobacterium tumefaciens containing pTi-T37, a nopaline-type Ti plasmid. Treatment of this cloned tumor tissue with kinetin at 1 mg/liter results in the formation of relatively normal-appearing shoots. These shoots can be induced to root and set viable seed. In contrast to BT37 tissue, the derived tissues are not phytohormone independent and do not produce nopaline. The reverted plants, like normal tobacco plants, are susceptible to infection by A. tumefaciens. This loss of tumorous traits is accompanied by the loss of most of the Ti plasmid sequences (T-DNA) found in BT37 DNA. Southern blot analysis indicates that the revertant tissues have lost the central portion of the T-DNA, which contains the "common DNA" sequences, a highly conserved region of the Ti plasmid that has been found to be incorporated into all tumors studied. Thus, these sequences appear necessary for oncogenicity and tumor maintenance and their loss is probably directly related to tumor reversal. The reverted plants as well as the plants obtained from seed, however, do retain sequences homologous to the ends of the T-DNA present in the parental teratoma. The persistence of foreign DNA sequences during the process of meiosis and seed formation has important implications for the possibility of the genetic engineering of plants.

Octopine synthase mRNA isolated from sunflower crown gall callus is homologous to the Ti plasmid of Agrobacterium tumefaciens

We have shown that the structural gene for octopine synthase (a crown gall-specific enzyme) is located in a central portion of the T-DNA that came from the Ti plasmid of agrobacterium tumefaciens and is expressed after it has been transferred to the plant cells. Polyadenylylated RNA was prepared from polysomes isolated from an octopine-producing crown gall callus and purified by selective hybridization to one of five recombinant plasmids. Each such plasmid contained a different fragment of T-DNA of pTi-15955 (octopine-type Ti plasmid). Purified mRNA was translated in vitro in rabbit reticulocyte lysates, and the translation products were immunoprecipitated with antibody against octopine synthase. Total and immunoprecipitated products were characterized by their molecular weights. A polypeptide of M(r) 40,000 (the same as authentic octopine synthase) was synthesized in vitro by crown gall mRNA selectively hybridized to three of the five fragments of T-DNA and precipitated with antibody against octopine synthase. This polypeptide was not immunoprecipitated with normal rabbit antibody nor was it synthesized when mRNA from the habituated callus was substituted. A mRNA 1500 bases long was detected when total mRNA was fractionated on an agarose gel, transferred to nitrocellulose, and used for hybridization to three of the five (32)P-labeled T-DNA fragments. This apparent mRNA for octopine synthase hybridized to the same three fragments of T-DNA as the mRNA for the M(r) 40,000 polypeptide and was not detected in the habituated callus.

Plasmid-dependent temperature-sensitive phase in crown gall tumorigenesis

Two methods have been used to show that the temperature-sensitive (ts) genes for plasmid maintenance located on pTiC58 are responsible for the presence of a specific 37 degrees C ts period during crown gall tumorigenesis. Tumors induced by Agrobacterium tumefaciens strain C58 become resistant to 32 degrees C by 96 hr after infection, indicating that the "inception phase" of crown gall is complete at that time. However, C58 tumors remain sensitive to 37 degrees C until 168 hr after infection. When pTiC58 is replaced in strain C58 by a plasmid that is temperature resistant for maintenance within the bacterium at 37 degrees C (B(6)806) the tumors induced by the new strain (A277) become resistant to 37 degrees C by 96 hr after infection. Furthermore, when pTiC58 is selected for temperature resistance in strain C58 at 37 degrees C, the tumors induced by the new strain, C58(TR), become resistant to 37 degrees C approximately 40 hr earlier than do tumors induced by the parent strain C58. These results prove that the 37 degrees C ts period (96-168 hr after infection) is coded for ts plasmid maintenance genes located on pTiC58. Incorporation of [(3)H]-thymidine into pTiC58 in strain C58 is specifically inhibited at 37 degrees C compared to chromosomal DNA and is not inhibited at 32 degrees C. The data presented support a mechanism in which the 37 degrees C, ts period between 96 and 168 hr after infection is due to the requirement for the plasmid-coded maintenance genes involved in plasmid replication within incipient tumor cells. The fact that the 37 degrees C ts period ends after 168 hr indicates a transient requirement for the ts gene product, perhaps due to the stable integration of plasmid DNA into plant genetic elements by that time.

Requirement for chemotaxis in pathogenicity of Agrobacterium tumefaciens on roots of soil-grown pea plants

Agrobacterium tumefaciens Tn5 mutants deficient in chemotaxis to root exudates were used to study the significance of chemotaxis in crown gall pathogenesis. Mutants deficient in motility and in chemotaxis were fully virulent when inoculated by direct immersion in inoculum, followed by growth for 2 weeks in moist growth pouches. Ability of mutant bacteria to move through soil to infect roots was tested by planting wounded seedlings into air-dried soil or sand that had been infested with inoculum. Mutant bacteria were almost as virulent as the parent on plants grown in sand but were avirulent on soil-grown plants.

Selective and accurate initiation of transcription at the T-DNA promoter in a soluble chromatin extract from wheat germ

An in vitro assay system was developed for accurate transcription of the octopine type T-DNA gene in a wheat germ extract. The system consists of the protein fraction extracted from the chromatin of wheat germ, substrates and exogenously added DNA. Specific initiation at the promoter was determined by a combination of primer extension analysis and size analysis of the transcripts synthesized from DNA templates of various molecular sizes. Synthesis of the transcripts was sensitive to alpha-amanitin. With truncated DNA templates containing the intact promoter and the proximal transcribing region of several hundred base pairs of the T-DNA, run-off transcripts of the expected size originating at the authentic promoter were synthesized together with relatively small amounts of prematurely terminated RNA molecules. On fractionation of the chromatin protein extract by DEAE-cellulose column chromatography, the fraction eluted with 0.3 M KCl showed no activity by itself for specific initiation of transcription at the promoter by RNA polymerase II. The activity was however restored by adding the fraction eluted with 0.15 M KCl, and the reconstituted RNA polymerase fraction correctly initiated transcription at the authentic promoter.

Functional domains of a T-DNA promoter active in crown gall tumors

Promoter domains required for transcriptional expression of the 780 gene of T-right (pTi15955) were identified by deletion mutagenesis. Accurate quantitation of transcriptional activity of a series of 5' and internal deletion mutants was achieved by using a double gene vector containing a reference 780 gene as an internal standard. Results of the 5' deletions delineated an activator element located between -440 and -229 base pairs (bp) from the start of transcription. Removal of this region resulted in a 100-fold decrease in promoter activity. Two relatively small internal deletion/substitution mutations at positions -74 to -76 and -98 to -112 reduced promoter activity to 38 and 42%, respectively. In most cases large-scale internal deletions (38 to 151 bp) occurring in various locations from positions -12 to -348 bp caused a significant loss in major promoter activity. However, three internal deletions starting at position -37 and extending upstream as far as -153 bp either had little effect on transcriptional activity or resulted in increased activity. Removal of the TATA motif drastically reduced promoter activity to less than 0.1% of the wild type. A minor start of transcription was detected 60 bases upstream from the major transcriptional start site. This minor promoter shares the same activator element as the major promoter for full activity. Deletion and insertion mutations downstream of the minor promoter TATA demonstrated the role of the TATA box in positioning the start of transcription.

Chromatin structure of integrated T-DNA in crown gall tumors

We have investigated the chromatin structure of the integrated T-DNA in two N. tabacum crown gall tumor lines, and compared the results to those obtained in a previous study of the methylation patterns of these same integrated DNA sequences (Gelvin et al., Nucleic Acids Res. 11:159-174, 1983). The E9 octopine-type tumor contains a single copy of TL, whose transcription is essential for tumor maintenance, and 15-30 copies of TR, a non-essential region. The HT37#15 nopaline type teratoma contains a single copy of the nopaline T-DNA. All these integrated sequences can be found associated with nucleosomes, although the diffuse nature of the nucleosome bands on Southern transfers implies an 'open' chromatin conformation. In addition, all the sequences are more sensitive to digestion with deoxyribonuclease I than the bulk of the chromatin. We present evidence suggesting that, despite the previously published data that the majority of copies of the TR-DNA are highly methylated at the sequence CCGG whereas the TL-DNA is not, the majority of copies of the TR-DNA in the E9 tumor line are in the same chromatin conformation as TL. These data therefore suggest that most of the copies of TR-DNA are likely to be transcriptionally competent.

Functional domains of a T-DNA promoter active in crown gall tumors

Promoter domains required for transcriptional expression of the 780 gene of T-right (pTi15955) were identified by deletion mutagenesis. Accurate quantitation of transcriptional activity of a series of 5' and internal deletion mutants was achieved by using a double gene vector containing a reference 780 gene as an internal standard. Results of the 5' deletions delineated an activator element located between -440 and -229 base pairs (bp) from the start of transcription. Removal of this region resulted in a 100-fold decrease in promoter activity. Two relatively small internal deletion/substitution mutations at positions -74 to -76 and -98 to -112 reduced promoter activity to 38 and 42%, respectively. In most cases large-scale internal deletions (38 to 151 bp) occurring in various locations from positions -12 to -348 bp caused a significant loss in major promoter activity. However, three internal deletions starting at position -37 and extending upstream as far as -153 bp either had little effect on transcriptional activity or resulted in increased activity. Removal of the TATA motif drastically reduced promoter activity to less than 0.1% of the wild type. A minor start of transcription was detected 60 bases upstream from the major transcriptional start site. This minor promoter shares the same activator element as the major promoter for full activity. Deletion and insertion mutations downstream of the minor promoter TATA demonstrated the role of the TATA box in positioning the start of transcription.

Initial interactions of Agrobacterium tumefaciens with plant host cells

Infections of wounded dicotyledonous plants by Agrobacterium tumefaciens result in the formation of crown gall tumors. The initial step in tumor formation is the site-specific attachment of the bacteria to the host cells. The mechanism of recognition and attachment in this interaction has been studied in detail. Current information on the nature of the bacterial binding sites, the nature of the host receptors, the role of bacterial cellulose fibrils, and the genetics of bacterial attachment will be summarized, and a model for the attachment of Agrobacterium to host cells will be presented.

Site-specific mutagenesis in the TR-DNA region of octopine-type Ti plasmids

Site-specific insertion and deletion mutations affecting all six of the eukaryotic-like genes in the TR-DNA region of the octopine-type Ti plasmids pTil5955 or pTiA6 have been generated. None of the mutations affected virulence or tumor morphology on sunflower. Mutations in the coding regions of two of the genes resulted in tumors without any detectable mannopine, mannopinic acid or agropine, and mutations in either the coding region or in the 3' untranslated region of a third gene eliminated biosynthesis of agropine, but not mannopine or mannopinic acid. Detection of two previously unobserved silver nitrate-positive substance in tumors incited by one of the mutant strains, together with data on the presence of opines in tumors incited by coinoculation with mixtures of different mutant strains, allowed us to propose the functional order of all three genes involved in the biosynthesis of mannopine, mannopinic acid and agropine. TR-DNA was absent in tumors incited by anAgrobacterium tumefaciens strain harboring a Ti plasmid in which the right border of the TR-DNA region was deleted.

Map locations of five transcripts homologous to TR-DNA in tobacco and sunflower crown gall tumors

Polyadenylated RNA from two octopine type tumor lines (E1, PSCG-15955) was analyzed by RNA blot hybridization and shown to contain five major transcripts homologous to TR DNA. In tobacco E1 tissue, the molecular weights of the TR homologous RNAs are 1.65 kb, 1.55 kb, 1.45 kb, 1.05 kb, and 0.78 kb. The 5' - and 3'-termini of each of the five E1 tumor transcripts were determined by S1 nuclease hybrid protection mapping. The polarity of transcription for the 0.78, 1.05 and 1.65 kb RNAs is from left to right, while the 1.55 and 1.45 kb RNAs are transcribed from right to left. Although we see the same size transcripts in sunflower PSCG-15955 tissue (with the exception of a 0.89 kb RNA in place of the 1.55 kb transcript of E1) there is an apparent difference in the relative abundance of the various RNAs between the two tumor lines.

Induction and in vitro culture of soybean crown gall tumors

Induction of crown galls on 4-6 week old soybean (Glycine max (L.) Merr.) plants cultured in growth chambers was obtained with Agrobacterium tumefaciens strains C58, T37 and ACH5. The crown galls were isolated and cultured in vitro as sterile callus and liquid suspension cultures. Transformation was tested by opine tests and by molecular hybridization of restricted cell DNA with T-DNA fragments. Protoplasts were isolated from suspension cultures. Transformed protoplasts regenerate cell walls, divide and form calli without an exogenous supply of hormones.

Site-directed mutagenesis in Escherichia coli of a stable R772::Ti cointegrate plasmid from Agrobacterium tumefaciens

The host range of an octopine Ti plasmid is limited to Rhizobiaceae. This has been extended also to Escherichia coli in the form of a stable cointegrate with the wide-host-range plasmid R772. Its structure was studied by constructing a physical map of R772 and of the R772::pTiB6 cointegrate. An insertion sequence present in R772, called IS70, turned out to be involved in cointegrate formation. We found one intact copy of IS70 and a small segment of IS70, respectively, at the junctions of R772 and Ti DNA. The absence of a complete second copy of IS70 is a likely explanation for the stability of the cointegrate plasmid. A procedure for site-directed mutagenesis of this cointegrate plasmid in E. coli is described. The effect of mutations in the Ti plasmid part can be studied subsequently by transferring the cointegrate into Agrobacterium tumefaciens. The advantage of this procedure for Ti plasmids over other methods used at present is discussed.

Mutational analysis of the virulence region of an Agrobacterium tumefaciens Ti plasmid

Forty-nine Tn3 and Tn5 transposition insertion mutations were introduced into the virulence region of the pTiA6NC plasmid of Agrobacterium tumefaciens. Five Tn5 transposition mutations from an earlier study (D. Garfinkel and E. Nester, J. Bacteriol. 144:732-743, 1980) were also mapped more accurately. These mutations defined five separate loci within the virulence region. Two Tn3 insertions into one of these loci, virA, result in a strain which is only weakly virulent; however, a Tn5 insertion into this locus eliminates virulence. One Tn5 insertion into another locus, virC, results in a strain which is weakly virulent. Two additional Tn5 insertions into this locus eliminate virulence. Insertions into the remaining three loci eliminate virulence entirely.

Methylation of the T-DNA in Agrobacterium tumefaciens and in several crown gall tumors

Methylation of the T-DNA in Agrobacterium tumefaciens and in four octopine-type (A6S/2, E9, 15955/1, 15955/01) and one nopaline-type (HT37#15) crown gall tumors was investigated using the isoschizomeric restriction endonucleases Msp I and Hpa II. T-DNA in the octopine-type Ti-plasmid pTiB6(806) was not methylated at the sequence 5'CCGG3' in Agrobacterium. With two possible exceptions, neither was the T-DNA of the nopaline-type Ti-plasmid pTiT37 methylated in the bacterium. In all tumor lines investigated, at least one copy of the T-DNA was not methylated. DNA methylation was not detected in the lines A6S/2, 15955/1, HT37#15, and the TL region of E9. DNA methylation of some copies of TR in the E9 tumor line, and possibly in the 15955/01 line, was detected. The methylation of some copies of TR in the E9 line may indicate that not all copies of TR are transcribed in this tumor.

Influence of a crown-gall tumor initiation enhancer on bacterial attachment to the host plant cell wall

The competitive activities of different plant cell walls upon Agrobacterium tumefaciens attachment have been studied in vitro by means of two crown-gall tumor initiation assays. The low or high susceptibility of different plant species is independent of their capacity to cause bacterial cells to adhere to specific sites on the plant cell walls. However, the attachment properties of cell wall fragments derived from Helianthus cotyledons seem to be age-dependent. It is found that a tumor initiation enhancer, present in extract fractions derived from highly susceptible plants and closely related with the competence for tumor formation, does not influence bacterial adherence. The two steps, attachment and the step by which the tumor initiation enhancer is involved, clearly differ in the processes leading to the transformation of a normal cell into a tumor cell.

Complementation analysis of Agrobacterium tumefaciens Ti plasmid mutations affecting oncogenicity

A wide host range cosmid vector has been constructed by insertion of the lambda cos site into the plasmid pRK2501. This cosmid, which is maintained in Agrobacterium tumefaciens and is compatible with the Ti plasmid, has been used to make a clone bank of the A. tumefaciens pTiA6 plasmid. Several pTiA6 cosmids have been used to complement Tn5-induced Ti plasmid mutations. Five avirulent mutations which map outside of the region of the plasmid maintained in plant tumours (T-DNA) could be complemented in a trans orientation. Two mutations which are located on a single HpaI restriction fragment outside of the T-DNA, as well as three mutations which map within the T-DNA region, could not be complemented in a trans orientation in a REC- host.

T-DNA of pTi-15955 from Agrobacterium tumefaciens is transcribed into a minimum of seven polyadenylated RNAs in a sunflower crown gall tumor

Northern blot hybridization analysis of polysomal polyadenylated RNA isolated from sunflower crown gall tumor PSCG-15955 demonstrated that a minimum of seven RNAs were transcribed from T-DNA of pTi-15955 from Agrobacterium tumefaciens. The sizes of the T-DNA transcripts were 1.8, 1.6, 1.5, 1.1, 1.0 kilo bases (kb) and two transcripts of 0.8 kb long. The relative abundance of these polyadenylated RNAs varied greatly, the 1.0 kb RNA being the most abundant and the 1.6 kb RNA being the least abundant. Assignment of map locations of the seven polyadenylated RNAs indicated that the conserved region of T-DNA which may play a central role in tumorigenesis contained four RNAs of 1.8, 1.1, 0.8(a) and a portion of 0.8(b) kb long.

Sizes and map positions of several plasmid-DNA-encoded transcripts in octopine-type crown gall tumors

The sizes and relative map positions of RNA molecules encoded by the plasmid DNA of several octopine-type tobacco crown gall tumors were determined by blot hybridization. At least six discrete polyadenylylated RNAs (sizes 0.73-1.75 kilobases) were detected in octopine-producing tumors (lines A6S/2, E9, and 15955/01). In one tumor (line 15955/1) in which octopine could not be detected, one of the RNA species was missing and another was diminished in abundance. Evidence is presented suggesting that the transcripts are encoded entirely by the plasmid DNA and do not originate from the surrounding plant DNA sequences.

Expression of plant tumor-specific proteins in minicells of Escherichia coli: a fusion protein of lysopine dehydrogenase with chloramphenicol acetyltransferase

Fragment EcoRI 7 from Ti-plasmid pTi Ach5, a part of the T-DNA in octopine tumors, was cloned in both orientations into pACYC184 and expressed in E. coli minicells. The cells synthesized four proteins from four different coding regions on EcoRI 7. Two of the proteins (Mr 25.000 and 26.000) were expressed with promoters from the Ti-plasmid fragment, while transcription for the two other proteins (Mr 18.000 and 74.000) started with a promoter on pACYC184. The Mr 18.000 protein represented a fusion product between chloramphenicol acetyltransferase (CAT) on pACYC184 and a part of lysopine dehydrogenase (LpDH), the enzyme synthesizing octopine and lysopine in plant tumor cells. The results suggest that E. coli minicells are a valuable system to study the proteins coded for by the T-region of Ti-plasmids.

Agrobacterium tumefaciens RNA polymerase: a new purification procedure and a study of the stable binding sites on homologous deoxyribonucleic acid

RNA polymerase (RNA nucleotidyltransferase, EC 2.7.7.6) of Agrobacterium tumefaciens has been purified according to a fast and efficient procedure. The method involves only two chromatographic steps and yields a highly active enzyme. The RNA polymerase was studied with respect to the ability to bind its homologous genome. A. tumefaciens deoxyribonucleic acid (DNA) binds the enzyme even when fragmented at undergenic size (300 base pairs). The general binding is unspecific and very labile at low concentrations of heparin (0.66 micrograms/mL). The number and distribution of the stable binding sites, class A sites [Hinkle, D., & Chamberlin, M. J. (1972) J. Mol. Biol. 70, 157-185], have been calculated from the heparin-induced dissociation kinetics of binary complexes formed between the enzyme and DNA fragments of various sizes. A total of 3.5 x 10(3) class A sites (forming binary complexes with a half-life of 16.6 min) are present on A. tumefaciens genome, a large number of which show a distribution of 800-1000 base pairs. The rest have a more widely spaced distribution. The interactions between Escherichia coli RNA polymerase and the A. tumefaciens template have also been examined, and it has been observed that E. coli holoenzyme forms stable complexes with a shorter half-life and recognizes a lower number of class A sites on A. tumefaciens genome.

Transcription of T-DNA in octopine and nopaline crown gall tumours is inhibited by low concentrations of alpha-amanitin

Highly purified and physiologically active nuclei were isolated from four different octopine and nopaline crown gall lines. These nuclei exhibited a high endogenous RNA synthesizing activity involving all three RNA-polymerases I, II and III. Isolated nuclei were shown by Southern blotting to synthesize T-DNA specific RNA. This synthesis was shown to be sensitive to actinomycin D and therefore to be DNA-dependent. The transcription of the T-DNA was also inhibited for more than 90% by low concentrations of alpha-amanitin (0.7 micrograms/ml) indicating that the T-DNA, although from bacterial origin, is transcribed by the host RNA polymerase II.

Strain-dependent temperature-sensitive phase in crown gall tumorigenesis

The effect of high temperature treatments on the early stages of crown gall tumorigenesis in sunflowers was investigated. Treatments of 32 C initiated at various times during the first ten days after infection had a similar effect on tumors induced by Agrobacterium tumefaciens strains B(6) and C58. Tumor growth was sensitive to 32 C until 60 to 72 hours after infection and was stimulated by 32 C after that time. Therefore, the "inception phase" for both C58 and B(6)-induced tumors ends between 60 to 72 hours after infection. In contrast, B(6) and C58 tumors varied in their response to 37 C treatments during the first 168 hours after infection. Both C58 and B(6) tumors were sensitive to 37 C during the first 72 hours; however, B(6) tumors became resistant to 37 C after 96 hours, whereas C58-induced tumors remained sensitive until 144 to 168 hours after infection.The growth rate of C58 and B(6) tumors in plants moved to 32 C at 90 hours after infection was the same. B(6) tumors in plants moved to 37 C at 90 hours after infection also continued to grow rapidly, whereas C58 tumors in plants moved to 37 C at 90 hours exhibited a complete cessation of tumor growth. The 37 C temperature-sensitive period specific to C58 tumors ceases by 168 hours after infection. This indicates that the temperature-sensitive functions are no longer required after 168 hours. The possible significance of this work with regard to the presence of a temperature-sensitive plasmid, pTiC58, in strain C58 and the mechanism of tumor-inducing plasmid DNA maintenance in incipient tumor cells is discussed.