首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary lamB, the structural gene for receptor, is the second gene of the malK-lamB operon in the malB region of the Escherichia coli K12 chromosome. lamB is essentially not expressed in the absence of an active malT gene product, the activator or the maltose regulon. A malT strain is resistant to phage . We show that: (i) Introduction of rho mutations in malT mutants restores lamB expression to a level sufficient to render the strain sensitive to phage ; (ii) This restoration is not dependent on the main promoter of the malK lamB operon. It depends on the distal part of the malK gene.We propose that rho inactivation unmasks the activity of a promoter located near the distal end of malK. Experiments with Mu insertions in gene malK suggest that in the (-) orientation a Mu promoter is also able to allow lamB expression in a rho background.  相似文献   

2.
3.
Summary Several strongly polar mutations in the omega region of the z gene of the lac operon result from insertions consisting of only two specific sequences of DNA, one about 870 and the other 1170 nucleotide pairs long (based on single-strand measurements). No sequence homology was detected between the shorter (IS1) and longer (IS3) insertions. The IS1 insertion was shown to possess a specific attachment site, but it can be inserted with either orientation at several sites in the z gene. Four insertion sites in the omega region of gene z were identified and the position of the lac5 substitution and the SR2 deletion in the plac DNA were determined by heteroduplex mapping.  相似文献   

4.
Approximately 4200 nucleotides of the 16S/23S rDNA spacer and the 5 region flanking therrn operon of the plastid chromosomes representing the five basic, phylogenetically relatedEuoenothera plastomes were sequenced and compared. The sequences that harbor the putative replication origins are almost identical except for a 785-bp intercistronic segment between the genes for the 16S rRNA andtrnI. Differences are mainly caused by insertions/deletions and duplications; the predicted potential for formation of quite extensive secondary structure differs among the plastomes. Unexpected intraplastome variation has also been noted. Furthermore, the sequence-based and published genetically deduced plastome pedigrees differ significantly.  相似文献   

5.
Summary Entry of DNA from phages particles into rMal- mutants of Escherichia coli K-12 is shown to be due to two distinguishable processes. One, residual transduction, results from a low level expression of lamB. The other one, background transduction, is independent of gene lamB.Interpretations are presented for these results. It is proposed that residual transduction is due to a weak promoter pB3 located within or near the distal part of the gene preceeding lamB in the same operon. It is proposed that background transduction is due to a secondary receptor structure for phage . Finally a tentative hypothesis relating pB3 to insertion sequences is presented.  相似文献   

6.
Non-random distribution of deletion endpoints in the gal operon of E. coli   总被引:3,自引:0,他引:3  
Summary The physical distances between endpoints of deletions in the gal operon of dgal phages previously isolated and mapped by genetic methods have been measured by electron microscopy of heteroduplex DNA. Thus, the galT and galK sites previously mapped by genetic methods, may be assigned to 13 and 4 intervals, respectively, of known physical lengths. The physical data clearly show a nonrandom distribution of these deletion endpoints.On the other hand, a large number of deletions in the gal operon obtained as survivors of a cI857 lysogenic strain at 42°C also show a non-random distribution of endpoints of deletions in the gal genes. There are at least two sites in the gal genes at which we observed a clustering of endpoints of deletions within the same regions of dgal del-phages and in the bacterial deletion mutants.  相似文献   

7.
O0 and strong-polar mutations in the gal operon are insertions   总被引:40,自引:0,他引:40  
Summary Three dg phages carrying strong-polar mutations in the gal operon are denser than the corresponding phages carrying the wildtype gal operon or reversions of the mutations to the Gal + phenotype. The latter phages have the same density. It is concluded that these strong-polar mutations are insertions of DNA into the gal operon.The amount of inserted DNA is different in the three mutations and is calculated to be 450, 1,080 and 1,800 nucleotide pairs respectively.The strong-polar phenotype is also found in a mutant supplied by A. Taylor which carries a Mu-1 phage integrated into the transferase gene.  相似文献   

8.
Summary To study the excision of bacteriophage Mu at the DNA sequence level, the Mu-derived phage placMu3 was transposed to the transcribed but non-translated leader region of a plasmid-borne tetracycline (tet) resistance gene. Revertants (excision products) were then selected by Tet+ restoration of Tet+ and characterized. Of 21 independent Tet+ revertants, 17 contained simple deletions of most or all of placMu3, while the other four contained more complex rearrangements in which one end of placMu3 had been transposed, and most of the prophage had been deleted. The deletion endpoints were found in short direct repeats in each of the complex rearrangements and in 11 of the 17 simple deletion excisants. The results suggest models of slipped mispairing of template and nascent DNA strands facilitated by proteins of the Mu transposition machinery.  相似文献   

9.
Summary The 5-proximal trp leader RNA segment (about 5S) decays at 2 to 3 times slower rates than the distal trp mRNA sequence. This has been demonstrated by employing the deletion mutants which lack a large portion of the structural genes but retain the promoter-proximal region of the trp operon. Relative stability of the leader RNA is not merely due to the presence of an untranslatable region in the segment; the internal untranslatable segment of trp mRNA downstream from the nonsense alteration site of a double mutant trpAD28·trpE9758 decays as fast as the normal trp mRNA sequence. These results suggest that the trp mRNA is endonucleolytically cleaved to yield the small 5-proximal leader RNA segment before the distal mRNA decays and that the leader RNA sequence is not subject to usual mode of mRNA decay in the 5 to 3 direction.  相似文献   

10.
Summary Six deletion mutants of temperate Bacillus subtilis phage 105 have been isolated on the basis of their increased resistance to chelating agents. The size and position of the deletions was determined by electronmicroscopy of DNA heteroduplexes. All deletions are located in a region about 55–70% from one end of the DNA molecule, in the right half of the known genetic map of the phage. The segment 55–65% does not contain any genes essential for lytic growth or lysogenization. A gene(s) for immunity is located in a segment 65–70% from the left end.By electronmicroscopy of partially denatured 105 DNA two A-T rich regions have been localized in the right half of the molecule. One of these regions falls within the non-essential 55–65% DNA segment.  相似文献   

11.
The 663 amino acid Mu transposase protein is absolutely required for Mu DNA transposition. Mutant proteins were constructed in vitro in order to locate regions of transposase that may be important for the catalysis of DNA transposition. Deletions in the A gene, which encodes the transposase, yielded two stable mutant proteins that aid in defining the end-specific DNA-binding domain. Linker insertion mutagenesis at eight sites in the Mu A gene generated two proteins, FF6 and FF14 (resulting from two and four amino acid insertions, respectively, at position 408), which were thermolabile for DNA binding in vitro at 43°C. However, transposition activity in vivo was severely reduced for all mutant proteins at 37°C, except those with insertions at positions 328 and 624. In addition, site-specific mutagenesis was performed to alter tyrosine 414, which is situated in a region that displays amino acid homology to the active sites of a number of nicking/closing enzymes. Tyrosine 414 may reside within an important, yet non-essential, site of transposase, as an aspartate-substituted protein had a drastically reduced frequency of transposition, while the remaining mutants yielded reduced, but substantial, frequencies of Mu transposition in vivo.  相似文献   

12.
Summary Phage Mu has been inserted into the structural gene for cytidine deaminase (cdd). By the use of phage (lac, Mu) the promoter for the cdd gene has been fused to lacZ. In these strains lacZ expression is regulated by the cytR repressor protein and is therefore induced by cytidine. The fusion strains were used for the isolation of cddo mutants. Plaque forming phages carrying the different cdd-lacZ fusions were isolated. Studies of the cdd-Mu strains showed that the cdd gene is transcribed clockwise with respect to the Escherichia coli map.  相似文献   

13.
14.
Summary The oligopeptide permease is encoded by at least four genes which are transcribed as a single operon. We cloned and characterized this operon from Salmonella typhimurium, as well as the flanking genes, tonB, ana and a new gene, cwd, which affects cell wall synthesis. We correlated the physical map of opp DNA with a detailed genetic map of the opp operon and the individual opp genes were accurately located with respect to various restriction sites by Southern blotting. The region of the chromosome near opp was found to be highly unstable with deletions arising at a high frequency. The operon also contains hot-spots for IS1 and IS5 insertions.  相似文献   

15.
Summary A deletion of phage P2, del6 (L.E. Bertani, 1980), thought to remove the structural gene int, and a deletion/substitution, vir94, thought to remove genes int, C and cox, were mapped by electron microscopy, using the heteroduplex technique.Four independent deletion/substitution mutations, all affecting the regulatory region of P2, were compared in all possible combinations with the same technique: two showed sequence homology in their substitution DNA. The results confirm the model proposed for the origin of these mutants, analogous to that for the origin of transducing variants in phage , but suggest in first approximation that the exchange between the P2 DNA and the chromosome of the host bacterium may occur at several different bacterial sites.A map of the regulatory region of P2, based on all data available from the study of deletions and insertions, is presented.  相似文献   

16.
Summary The regulatory gene, glnF, of Escherichia coli was fused to the structural genes of the lac operon by use of the hybrid Mu phage derivative Mudl (Ap lac). Analysis of two of these fusions showed that the glnF gene is expressed constitutively, i.e., independent of either the nitrogen source in the growth medium or the availability of the glnA, glnL, glnG or glnF functional gene products. The orientation of the Mud1 (Ap lac) insertions was determined by chromosome mobilization in F-merogenotes carrying either of the two glnF:: Mud1 chromosomal insertions isolated, and either one of a pair of F'lacZ:: Mucts62 episomes; the two episomes differing in that their Mucts62 insertions are located in opposite orientations with regard to lacZ. The direction of chromosome mobilization by the Hfrs that were probably formed via Mu homology demonstrated that orientation of the glnF gene is clockwise relative to that of the chromosome.  相似文献   

17.
Summary A novel plasmid vector, pAMH70 carrying both the lamB and nusA genes of Escherichia coli K12 was constructed. Introduction of this plasmid into Salmonella typhimurium LT2 renders this bacterium both sensitive to adsorption and able to sustain growth and lysogenization by . Using this strain as a recipient, stable gene fusions to the gene encoding a major outer membrane porin protein OmpC, were constructed with a vehicle placMu. To confirm the actual site of fusions they were genetically mapped and transducing phages carrying the ompC-lacZ fusion were isolated and relysogenized. The fusions were also shown to be to ompC by their regulatory properties.  相似文献   

18.
Summary Deletion and point mutants defective in the glpT-dependent sn-glycerol-3-phosphate transport system were isolated and located on the Escherichia coli chromosome. They mapped in glpT in the clockwise order gyrA, glpA, glpT at around 48 min on the Escherichia coli linkage map. The mutations within glpT were ordered by deletion mapping, three factor crosses, and by crosses involving transducing bacteriophages carrying glpT-lac operon fusions. Results obtained using these fusion phages indicated that glpT is transcribed in the counterclockwise direction on the E. coli linkage map.Complementation analysis using these mutants revealed only one complementation group. Thus, one gene is necessary and sufficient for the proton motive force-dependent sn-glycerol-3-phosphate transport system.  相似文献   

19.
Summary The partially circularly permuted, terminally redundant structure of the DNA of phage H has been confirmed by a cleavage map for the restriction enzymes PstI, ClaI, BglII, HindIII, and, partially, BamHI.Six variants of phage H have been isolated from 71 single plaques. Their genomes differ by several insertions, a deletion, and an inversion of a DNA segment with a minimal length of 11 kb. The inversion occurs with high frequency in variants carrying at the flanks of the invertible DNA in verted repeats of a 1.8 kb DNA element which shares sequence homology with the DNA of H. halobium and may be involved in the extreme variability of its genome.  相似文献   

20.
Summary A selection procedure using Mn2+ is described. A high percentage of the Mn2+ resistant mutants had constitutive iron transport systems. By P1 transduction, and complementation with the cloned fur gene it could be shown that nearly all the mutants constitutive in the expression of the operon fusion fiu::placMu were only defective in fur. High concentrations of manganese inhibited the derepression of an iron-regulated lac operon fusion. In another iron-regulated lac operon fusion that was inducible by iron, manganese also induced the production of -galactosidase. Most of the fur mutants isolated (80%) were not able to grow on succinate, fumarate or acetate. After transformation with a fur + plasmid all 39 mutants tested were able to grow on succinate. In fur mutants the presence of succinate in the growth medium reduced succinate uptake rates by 50%–70%. Succinate dehydrogenase activity was reduced to 10% of that of the parent strain.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号