Expression of a retrovirus encoding human HPRT in mice

Transmissible retroviruses encoding human hypoxanthine phosphoribosyltransferase (HPRT) were used to infect mouse bone marrow cells in vitro, and the infected cells were transplanted into mice. Both active human HPRT-protein and chronic HPRT-virus production were detected in hematopoietic tissue of the mice, showing transfer of the gene. These results indicate the possible use of retroviruses for somatic cell therapy.

DNA replication and chromatin structure of simian virus 40 insertion mutants

Insertion of DNA segments into the nuclease-sensitive region of simian virus 40 alters both replication efficiency and chromatin structure. Mutants containing large insertions between the simian virus 40 origin of replication (ori site) and the 21-base-pair repeated sequences replicated poorly when assayed by transfection into COS-1 cells. Replication of mutants with shorter insertions was moderately reduced. This effect was cis-acting and independent of the nucleotide sequence of the insert. The nuclease-sensitive chromatin structure was retained in these mutants, but the pattern of cleavage sites was displaced in the late direction from the ori site. New cleavage sites appeared within the inserted sequences, suggesting that information specifying the nuclease-sensitive chromatin structure is located on the late side of the inserts. Accessibility to BglI (which cleaves within the ori site) was reduced in the larger insertion mutants. These results support the conclusion that efficient function of the viral origin of replication is correlated with its proximity to an altered chromatin structure.

Disruption of regulatory gene GAL80 in Saccharomyces cerevisiae: effects on carbon-controlled regulation of the galactose/melibiose pathway genes

In Saccharomyces cerevisiae, the transcriptional expression of the galactose-melibiose catabolic pathway genes is under the control of at least three regulatory genes, GAL4, GAL80, and GAL3. We have isolated the GAL80 gene and have studied the effect of a null mutation on the carbon-controlled regulation of the MEL1 and GAL cluster genes. The null mutation was achieved in vivo by replacing the chromosomal wild-type GAL80 allele with an in vitro-created GAL80 deletion-disruption mutation. Enzyme activities and RNA levels for the GAL cluster and MEL1 genes were constitutively expressed in the null mutant strain grown on glycerol-lactate and were higher than in the isogenic wild-type yeast strain when compared after growth on galactose. Carbon catabolite repression of the GAL cluster and MEL1 genes, which occurs at the level of transcription, is retained in the null mutant. Deletion of the GAL80 gene in a gal4 cell does not restore GAL cluster and MEL1 gene expression. The data demonstrate that (i) the GAL80 protein is a purely negative regulator, (ii) the GAL80 protein does not mediate carbon catabolite repression, and (iii) the GAL4 protein is not simply an antagonizer of GAL80-mediated repression.

Potential effects of renin activation on the regulation of renin production

In normal humans nearly half the renin in plasma and kidney is inactive. Human inactive renin can be activated by a variety of proteases and by exposure to low pH and is a putative biosynthetic precursor of renin, i.e., prorenin. Pulse-labeling studies in a human renin-secreting tumor suggest that renin is synthesized as a prepro- and proform, both of which are inactive. Using the cDNA probe to deduce the amino acid sequence of precursor renin from the nucleotide sequence of human kidney mRNA, the prosegment was estimated to be 46 amino acids long, similar to differences in molecular weight between active and inactive renin. In plasma of diabetic patients with nephropathy and the syndrome of hyporeninemic hypoaldosteronism, inactive renin levels are increased 3-5 times normal. The inability to activate renin in this syndrome strongly implies that conversion of inactive (pro-) renin to active renin may be physiologically relevant to active renin production. Furthermore, in normal humans profound stimulation of active renin can be accompanied by a reciprocal drop in circulating inactive renin levels. The beta-adrenergic system and prostaglandins are two major, but independent, mechanisms of stimulating renin release. Studies in our laboratory suggest that prostaglandins and the beta-adrenergic system may act at different sites in renin production: beta-stimulation may act at early steps in renin biosynthesis, while prostaglandins may act preferentially at later steps that possibly involve conversion of inactive to active renin. Proof of this hypothesis lies in purification of inactive renin to determine whether it is prorenin and in the use of the renin cDNA probe to study pre- vs. posttranslational events in renin processing.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of a signaling protein in bacterial sensing: behavioral effects of increased gene expression

A recombinant DNA approach has been used to study intracellular signaling in the bacterial sensing system. The Escherichia coli cheY gene, whose function is unknown, has been subcloned behind the synthetic inducible tac promoter. The resulting plasmid directs the synthesis of the Y protein in response to isopropyl beta-D-thiogalactoside, independent of its usual operon control. When this construct was introduced into wild-type and mutant cells, the Y protein caused a clockwise rotational bias in the flagellar motors. This effect was observed even in heavily biased counterclockwise strains lacking most of the central chemotaxis processing genes. The results show that the Y protein has a direct influence on flagellar rotation not requiring other processing genes of the sensing system. The Y protein appears to bind directly to a part of the flagellar motor, probably the flaA gene product, and it is probably the key element in biasing the motor toward the clockwise rotational direction.

Hyperrecombination at a specific DNA sequence in pneumococcal transformation

In pneumococcal transformation, recombination frequency between point mutations is usually proportional to physical distances. We have identified an aberrant marker belonging to the amiA locus that appeared to markedly enhance recombination frequency when crossed with any other markers of this gene. This mutation results from the C-to-A transversion in the sequence A-T-T-C-A-T----A-T-T-A-A-T. This effect is especially apparent for short distances as small as 27 base pairs. The hyperrecombination does not require the wild-type function of the pneumococcal gene for an ATP-dependent DNase (which is homologous to the product of the Escherichia coli recBC genes) or of the hex genes, which correct certain mismatched bases in transformation. The hyperrecombination is affected by the presence of nearby mismatched bases that trigger an excision-repair system. It is proposed that the mutation that shows hyperrecombination is sometimes converted to the wild-type allele at the heteroduplex stage of transformation.

BK virus-plasmid expression vector that persists episomally in human cells and shuttles into Escherichia coli

We describe a novel expression vector, pBK TK-1, that persists episomally in human cells that can be shuttled into bacteria. This vector includes sequences from BK virus (BKV), the thymidine kinase (TK) gene of herpes simplex virus type 1, and plasmid pML-1. TK+-transformed HeLa and 143 B cells contained predominantly full-length episomes. There were typically 20 to 40 (HeLa) and 75 to 120 143 B vector copies per cell, although some 143 B transformants contained hundreds. Low-molecular-weight DNA from TK+-transformed cells introduced into Escherichia coli were recovered as plasmids that were indistinguishable from the input vector. Removal of selective pressure had no apparent effect upon the episomal status of pBK TK-1 molecules in TK+-transformed cells. BKV T antigen may play a role in episomal replication of pBK TK-1 since this viral protein was expressed in TK+ transformants and since a plasmid that contained only the BKV origin of replication was highly amplified in BKV-transformed human cells that synthesize BKV T antigen.

Genetics of adeno-associated virus: isolation and preliminary characterization of adeno-associated virus type 2 mutants

We constructed insertion and deletion mutants with mutations within the adeno-associated virus (AAV) sequences of the infectious recombinant plasmid pSM620. Studies of these mutants revealed at least three AAV phenotypes. Mutants with mutations between 11 and 42 map units were partially or completely defective for rescue and replication of the AAV sequences from the recombinant plasmids (rep mutants). The mutants could be complemented by mutants with replication-positive phenotypes. The protein(s) that is affected in rep mutants has not been identified, but the existence of the rep mutants proves that at least one AAV-coded protein is required for viral DNA replication. Also, the fact that one of the rep mutant mutations maps within the AAV intron suggests that the intron sequences code for part of a functional AAV protein. Mutants with mutations between 63 and 91 map units synthesized normal amounts of AAV duplex DNA but could not generate single-stranded virion DNA (cap mutants). The cap phenotype could be complemented by rep mutants and is probably due to a defect in the major AAV capsid protein, VP3. This suggests that a preformed capsid or precursor is required for the accumulation of single-stranded AAV progeny DNA. Mutants with mutations between 48 and 55 map units synthesized normal amounts of AAV single-stranded and duplex DNA but produced substantially lower yields of infectious virus particles than wild-type AAV (lip mutants). The lip phenotype is probably due to a defect in the minor capsid protein, VPI, and suggests the existence of an additional (as yet undiscovered) AAV mRNA. Evidence is also presented for recombination between mutant AAV genomes during lytic growth.

Evidence for translational regulation of herpes simplex virus type 1 gD expression

We compared the rates of synthesis of herpes simplex virus type 1 glycoproteins C and D and quantitated the accumulation of translatable mRNA for each glycoprotein at various times after infection. The rate of synthesis of gD increased sharply early in the infection, peaked by 4 to 6 h after infection, and declined late in the infection. In contrast, the rate of synthesis of gC increased steadily until at least 15 h after infection. The levels of mRNA for both of these glycoproteins, as detected by hybridization and by translation in vitro, continued to increase until at least 15 or 16 h after infection. Synthesis of both gC and gD and their respective mRNAs was found to be sensitive to inhibition of viral DNA replication with phosphonoacetic acid. The finding that reduced amounts of gD were synthesized late in the replicative cycle, whereas gD mRNA continued to accumulate in the cytoplasm, argues that the synthesis of gD is regulated, in part, at the level of translation.

Lack of specific sequence requirement for DNA replication in Xenopus eggs compared with high sequence specificity in yeast

We examined the controversial question concerning DNA sequences required for replication in Xenopus eggs. First we used yeast to isolate ARS elements from the Xenopus genome. They show a striking sequence homology with the yeast ARS consensus sequence. The cloning vector and the ARS-containing plasmids replicate equally after injection into Xenopus eggs. Second, we compared a wide range of DNA templates from procaryotes and eucaryotes. All DNA molecules tested replicate as monomeric molecules, and the efficiency is proportional to their size for templates between 4 and 12 kb. Third, we re-examined two reports of replication origins from the Xenopus genome. In both cases, the vector and the recombinant molecules replicate equally under all conditions tested. The apparent lack of sequence specificity for replication in Xenopus eggs does not prevent the injected molecule from being under cellular temporal control of replication. These results are compared with those from yeast.

An EBNA-negative, EBV-genome-positive human lymphoblast cell line in which superinfecting EBV DNA is not maintained

A human B-lymphoid cell line, designated TG8, which does not express detectable levels of the EBV (Epstein-Barr virus)-associated nuclear antigen (EBNA), yet carries an average of one to two plasmid copies of the P3HR-1 EBV genome has been identified. TG8 can be superinfected by B95-8 EBV, resulting in up to 60-70% of the population becoming EBNA-positive and 20-30% of the incoming EBV genomes becoming circular by 48 hr postinfection. Neither EBNA expression nor the superinfecting viral DNA is maintained in the population. It is concluded that (1) superinfection of this EBV-genome-positive lymphoblast cell line leads to detectable EBNA expression and circularization of the incoming viral genome and (2) the incoming viral genome and detectable EBNA expression are selectively lost, whereas the endogenous viral plasmid DNA is maintained.

Differences in human alpha- and beta-globin gene expression in mouse erythroleukemia cells: the role of intragenic sequences

Human beta-globin genes introduced into mouse erythroleukemia (MEL) cells by DNA cotransformation are correctly regulated when erythroid cell differentiation is induced by dimethylsulfoxide (DMSO). In contrast, cloned human alpha-globin genes are efficiently transcribed in MEL cells prior to induction, and no increase in the level of alpha-globin mRNA is observed when the cells differentiate. These observations suggest that the mechanisms by which alpha- and beta-globin genes are activated during erythroid cell differentiation are fundamentally different. Analysis of the transcription of hybrid human alpha/beta-globin genes in MEL cells revealed that the sequences responsible for differences in transcription of the intact alpha- and beta-globin genes are located on the 3' side of the mRNA capping site of the two genes, suggesting that cis-acting regulatory sequences are located within the structural genes.

Deletion of an essential gene in Escherichia coli by site-specific recombination with linear DNA fragments

Deletion of an essential gene in Escherichia coli was accomplished by transformation of linear DNA fragments that have a Kanr gene segment flanked by sequences homologous to closely spaced regions on the E. coli chromosome. Selection for a double crossover within homologous sequences can effectively delete an entire gene. Cell viability is maintained by provision of the essential gene on a plasmid with a temperature-sensitive replicon, resulting in cells which have a temperature-sensitive phenotype.

Shuttle plasmids for Escherichia coli and Clostridium perfringens

Small plasmids which replicate in both Escherichia coli and Clostridium perfringens were made by recombining E. coli plasmid pBR322 with three different small (less than 4 kilobases) plasmids native to C. perfringens. Subsequently, two homologous, though distinct, tetracycline resistance determinants (tet) from other C. perfringens plasmids were cloned into them. Both tet systems made E. coli resistant to at least 5 micrograms of tetracycline per ml when resident on the shuttle plasmids. The shuttle vectors have been used to transform L-phase variants and autoplasts of C. perfringens. In the latter case, the intact transforming plasmid could be isolated from walled cells after cell wall regeneration. Reciprocal transformation experiments in which plasmid DNAs derived from E. coli or C. perfringens were used suggest that restriction barriers exist between these two organisms. The plasmids contain restriction enzyme recognition sites in locations which are useful for cloning experiments.

Introduction of human gamma 1 immunoglobulin genes into fertilized mouse eggs

A rearranged human gamma 1 immunoglobulin gene was introduced into fertilized mouse eggs. The phage Ch4A-VCE-gamma 1 was constructed by ligating an EcoRI and BglII fragment of pBR322-CESSV(CE-1) containing the VDJ region with an EcoRI and BamHI fragment of Ch4A-HIg gamma 1-10 containing the gamma 1 constant region. About 200 copies of Ch4A-VCE-gamma 1 genes were introduced into fertilized mouse eggs. Of 489 eggs injected with these genes, 319 survived and were transferred to oviducts of foster mothers. Thirtyeight mice were born and were screened for the presence of human gamma 1 immunoglobulin genes by Southern blot hybridization. Five of these 38 mice had integrated human gamma 1 immunoglobulin genes. None of the human gamma 1 copies in each mouse had undergone deletions or rearrangements as judged by the Southern blotting patterns for several restriction enzymes. Human gamma 1 gene was present in several different tissues. All the mice tested so far transmit the human gamma 1 gene to a fraction of their offspring in an autosomal dominant manner. Spleen cells from transgenic mice were analyzed for immunoglobulin production by reverse plaque assay or immunofluorescence staining of cytoplasmic immunoglobulin, but synthesis and secretion of human gamma 1 chains could not be detected. No human gamma 1 immunoglobulin mRNA was detected in the liver and spleen of a transgenic mouse. The presence of the human gamma 1 immunoglobulin gene appeared to have no effect on the expression of endogenous mouse immunoglobulin genes.

Epstein-Barr virus (P3HR-1) defective DNA codes for components of both the early antigen and viral capsid antigen complexes

A set of lambda phages containing overlapping fragments of Epstein-Barr virus (EBV) defective DNA has been cloned from P3HR-1-superinfected Raji cells. Mapping data obtained using these cloned DNA fragments confirmed the structure of P3HR-1 defective DNA previously deduced directly from virion DNA (M.-S. Cho, G. W. Bornkamm, and H. zur Hausen, 1984, J. Virol., in press). The ability of the cloned defective DNA fragments to induce EBV antigens in transfected baby hamster kidney (BHK) cells was tested using indirect immunofluorescence assays. Up to 5% of those cells receiving a defective DNA fragment BamHI-W'C' transiently expressed a de novo nuclear antigen which was identified as being a component of the EAD complex by its reactivity with characterized EBV-positive human sera. A 20-kb clone of P3HR-1 defective DNA (EcoRI-C1) was found to induce the synthesis of a component of the VCA complex. One percent of cells transfected with this clone showed cytoplasmic fluorescence when tested with either VCA+ human sera or EBV anti-VCA monoclonal antibody. Subcloning of the EcoRI-C1 fragment localized the VCA gene to a 4.1-kb segment which maps within the BamHI-A fragment of the standard genome. This segment contains a single large open reading frame of 2.6 kb (B. Barrell, A. Bankier, R. Baer, P. Biggin, P. Deininger, P. Farrell, T. Gibson, G. Hatfull, G. Hudson, S. Stachwell, and C. Sequin, 1984, Nature (London), in press). None of the defective DNA clones were capable of inducing EBV-specific nuclear antigens (EBNAs) which is consistent with the absence of the known EBNA coding regions from the defective genome.

The internal regulated promoter of the deo operon of Escherichia coli K-12

Previous studies of the structure and regulation of the deo operon in Escherichia coli have localized an internal regulated promoter, called deoP3, in front of the two distal genes in the operon. We report here the nucleotide sequence of the distal portion of the deoA, the deoA-deoB intercistronic region and the first part of the deoB gene, and show that deoP3 overlaps the distal segment of the deoA gene. The location of the internal promoter and the transcriptional start site were determined by means of 1) sequence homology to the consensus promoter sequence of E. coli, 2) high resolution S1 nuclease mapping of in vivo transcripts and 3) in vivo regulation of beta-galactosidase from low as well as high copy number P31acZ protein fusion vectors.

Initiation of plasmid R1 replication in vitro is independent of transcription by host RNA polymerase

A Sau3A fragment containing most of the repA gene of plasmid R1 has been cloned in the BamH1 site of the expression vector pAS1. One of the recombinants, pSO1, codes for a fused RepA' protein which is efficiently synthesized both in vivo and in vitro from transcriptional and translational signals of the vector. It is shown that following pSO1 promoted accumulation of RepA' in cell-free extracts of E. coli, in vitro replication of the R1 miniplasmid pKN182 can initiate and proceed uncoupled from further protein synthesis. Using this uncoupled system and also a M13mp9 based ori-R1 recombinant, pRD95, it is also shown that RepA' acts at the origin region of R1 to promote initiation of replication that is independent on transcription by host RNA polymerase. This is indicated by the insensitivity of pRD95 and pKN182 replication to rifampicin as well as to RNA polymerase antibodies. The properties of the uncoupled in vitro replication system are further described.

Differentiation-dependent chromatin alterations precede and accompany transcription of immunoglobulin light chain genes

We have studied the nature of chromatin alterations along immunoglobulin light chain (IgL) genes during B cell development using cultured murine cell lines. Employing a chromatin fractionation procedure on micrococcal nuclease-treated nuclei, we demonstrate that transcriptionally active k IgL chromatin lacks a canonical nucleosomal repeat and exhibits a pronounced association with insoluble nuclear material but is processed by nuclease to a soluble nucleosomal component that apparently lacks histone H1 and is enriched in high mobility group proteins. Of particular significance, utilizing a variant plasmacytoma cell line that has transcriptionally inactivated one k allele via a promoter deletion, we demonstrate that transcription per se is not responsible for these novel alterations. Furthermore, we show that the chromatin encompassing germline (unrearranged) and transcriptionally silent lambda IgL alleles in k-producing plasmacytomas exhibit some of the same unusual properties that are displayed by k alleles. Finally, we demonstrate that these alterations only occur in cell lines of the lymphocyte lineage that have progressed past the early pre-B cell stage; when inactive, both k and lambda IgL genes possess typical nucleosomal packaging and co-fractionate with histone H1-containing chromatin. These findings lead us to propose a model that predicts B cell stage-specific alterations in IgL chromatin prior to gene rearrangement and transcription.

In vitro transcription from the adenovirus 2 major late promoter utilizing templates truncated at promoter-proximal sites

We report that adenovirus 2 DNA sequences located between positions-66 and -51 upstream of the major late cap site (position +1) enhance transcription initiation from this promoter by up to 5- to 10-fold in HeLa whole cell lysates. This enhancing effect is template concentration-dependent and is abolished by truncation of the template immediately upstream of -66. Additionally, specific transcripts are not detected from templates truncated at +33 downstream of the cap site. These results define a minimum region of approximately 100 base pairs encompassing the transcription start site that appears to interact with the RNA polymerase II transcription complex during initiation. Analysis of the shortest runoff transcripts that can be synthesized in vitro revealed that RNAs as short as 50 nucleotides are quantitatively modified by guanylylation and methylation to cap 1 structures. In contrast, short RNAs containing guanylylated but unmethylated cap structures are not efficiently utilized as substrates by endogenous cap-methylating enzymes in the HeLa lysate. These findings, together with the observation that the synthesis of short transcripts is sensitive to the presence of the methyltransferase inhibitor S-adenosylhomocysteine, suggest that cap formation is a promoter-proximal event that occurs concomitantly with the synthesis of a nascent RNA polymerase II transcript.

Overproduction of a gastrointestinal hormone, secretin, in Escherichia coli cells and its chemical characterization

A cloned synthetic DNA fragment coding for 27-desamidosecretin (DAS), which differs from natural porcine secretin by the lack of the amide group at the carboxyl-terminal valine residue, was fused to the beta-galactosidase gene (lacZ) at the EcoRI site near the 3'-terminus of the gene. The fusion gene was efficiently expressed in Escherichia coli, yielding 1.15 X 10(6) fused-protein molecules per cell. After the treatment of the fused protein with cyanogen bromide, DAS was purified by a combination of ion-exchange column chromatography and reverse-phase high-performance liquid chromatography (HPLC). The structure of bacterial DAS was confirmed by tryptic mapping and amino acid composition analyses. The bacterial DAS was not amidated at its carboxyl-terminal valine residue. Nevertheless, it stimulated pancreatic secretion in rats as does authentic porcine secretin, indicating that the carboxyl-terminal amide is not essential to secretin activity.

One-step purification of hybrid proteins which have beta-galactosidase activity

A one-step purification method of hybrid proteins exhibiting beta-galactosidase activity, based on affinity chromatography in the presence of high salt concentration, is described. Starting from crude bacterial extracts, several milligrams of near-homogeneous proteins can be obtained in a few hours with an overall yield of 85 to 95%. The purified hybrid proteins can be used to obtain antibodies against the foreign portion of the protein fusion.

Plasmid vector for cloning in Streptococcus pneumoniae and strategies for enrichment for recombinant plasmids

A new plasmid, pLS101, was constructed for use as a vector for cloning in Streptococcus pneumoniae. This plasmid carries two selectable genes, tet and malM, each of which contains two or more restriction sites for cloning. Insertional inactivation of the malM gene allowed direct selection of TcRMal- clones containing recombinant plasmids. Other means of enriching a recipient population for cells containing recombinant plasmids were examined. The effect of removing vector terminal phosphate in attempts to clone heterogeneous DNA fragments, such as those from chromosomal DNA, was to abolish recombinant plasmid establishment altogether, presumably because donor DNA processing during entry into the cell prevented establishment of the hemiligated molecule. However, with homogeneous DNA fragments, such as those from plasmid or viral DNA, vector phosphate removal allowed enrichment for recombinant plasmids. In the cloning of heterogeneous DNA that was homologous to the recipient chromosome (i.e. chromosomal DNA from S. pneumoniae), recovery of recombinant plasmids could be enriched tenfold (relative to the regenerated vector) by the process of chromosomal facilitation of plasmid establishment. This involved an additional passage of the mixed plasmids in which interaction with the chromosome of plasmids containing chromosomal DNA inserts (i.e. recombinant plasmids) increased their frequency of establishment relative to the vector plasmid. An overall strategy for cloning in S. pneumoniae, depending on the nature of the fragment to be cloned, is proposed.

Structure and function of the yeast URA3 gene: expression in Escherichia coli

The expression of the cloned Saccharomyces cerevisiae URA3 gene in Escherichia coli on both plasmid and phage vectors was studied. Isolates of the gene from two different laboratory strains of yeast differ in their ability to be expressed in E. coli in the absence of external adjacent promoters of transcription. The DNA sequence of the two genes was determined and revealed several differences in the DNA flanking the structural gene. One base change alters the "Pribnow-box" of an E. coli promoter present in the yeast sequences. Three amber alleles of the yeast gene were also cloned from yeast. Two of the alleles could be suppressed in E. coli by a tRNA suppressor mutation. One of the amber alleles was determined to be a mutation in the seventh codon of the structural gene, thereby establishing the reading frame and extent of the coding sequence. The initiator codon of the reading frame encoding the URA3 structural gene is preceded by two other ATG codons in a different reading frame 61 and 79 bp away. The nearer ATG begins an open reading frame that overlaps the structural gene sequences by 17 bp. With the DNA sequence of the URA3 gene many of the common yeast vector plasmids are now completely known at the level of DNA sequence.

A technique for integrating any DNA fragment into the chromosome of Escherichia coli

We describe a technique that allows the insertion of any DNA fragment into the EcoRI-site-containing malPpa, the promoter of malPQ, one of the three maltose operons of Escherichia coli. DNA fragments were cloned into the unique EcoRI site of the pBR322-derived plasmid pOM40, which carries malPpa. In the next step these fragments were transposed into the chromosome by homologous recombination events occurring on both sides of malPp. Cells in which such insertion of the entire recombinant plasmid have occurred can be conveniently selected. Excision and curing of the vector plasmid could then occur spontaneously at a high frequency, leaving behind the inserted fragment that can be manipulated as any chromosomal marker. When the inserted fragment contains a properly positioned promoter, its promoting activity can be estimated by assaying amylomaltase, the product of malQ. When required, the inserted fragment can be easily transferred back onto pOM40. As examples of application we have transferred two different fragments into the chromosome of E. coli: one contained the ceaC-ceiC operon, which encodes colicin E3 and its immunity protein, and the other contained the lac promoter of E. coli.