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PubMed2026

Harnessing Id1 as a biomarker in a plasmid reporter system for cervical cancer.

Stagnancy of ten-year cervical cancer (CC) incidence in the U.S., despite screening advancements, suggests the need for new CC screening technologies. This study in preclinical CC models evaluated a diagnostic plasmid that induces expression of a reporter (secreted embryonic alkaline phosphatase, SEAP) through the control of cancer-specific promoter sequence (inhibitor of differentiation 1, Id1). The plasmid (pId1-SEAP) was used to transfect CC cells in vitro and characterize SEAP production based on Id1 expression. Western Blot and immunohistochemistry were used to establish Id1 expression in cell models and human tissues. Timed transfections in various conditions were used to correlate Id1 and SEAP expression. CC cell lines expressed increased normalized baseline Id1 (HeLa 3.0 ± 0.13, SiHa 2.9 ± 0.27, both P < 0.0001) compared to non-cancer 3T3 fibroblasts (1.0 ± 0.0). Normal cervical tissues had a mean Id1 staining value of 3E4 ± 3E4, while early- and late-stage CC tissues had increased mean Id1 staining (3E5 ± 1E5 P < 0.0001 and 2E5 ± 1E5 P = 0.0002, respectively). HeLa and SiHa lines produced increased normalized SEAP (0.63 ± 0.25 and 0.50 ± 0.10, P < 0.05) compared to 3T3 cells, both with pId1-SEAP (0.16 ± 0.058). As few as 12,500 pId1-SEAP transfected HeLa cells resulted in increased SEAP (3E4 ± 3E3 P = 0.004) compared to background (1E4 ± 4E2). SiHa xenograft ex vivo tumor transfected with 25 µg/µL pId1-SEAP produced significantly greater SEAP (21.7 ± 8.6, P = 0.0003) relative to muscle transfected in the same conditions (0.94 ± 0.24). pId1-SEAP can transfect CC cells to produce SEAP proportionally to endogenous Id1 expression, demonstrating its potential for additional studies in CC models.

Female↗

PubMed2026

Functional analysis of stem-loop structures within the SARS-CoV-2 5' untranslated region using a plasmid-based reporter system.

The 5' untranslated region (5'UTR) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contains highly conserved stem-loop structures that regulate viral gene expression. This study investigated the functional contributions of selected 5'UTR stem-loop elements to reporter gene expression using a plasmid-based mammalian expression system. Five constructs were tested using a non-integrating plasmid: the wild-type (WT) 5'UTR fused to GFP under the CMV promoter, and four deletion variants (ΔB, ΔC, ΔD, and ΔE) corresponding to deletions of stem-loop 4 (SL4), SL4.5, SL5, and SL5a, respectively. Following transfection into HEK293 cells, GFP fluorescence was quantified using a fluorescence microplate reader, and relative GFP transcript abundance was assessed by RT-qPCR. Deletion of SL4 (ΔB) resulted in marked reduction in both fluorescence and relative transcript abundance compared to WT construct, indicating substantially reduced reporter gene expression. In contrast, deletion of SL4.5, SL5, or SL5a did not produce the pronounced reduction observed for ΔB, although descriptive RT-qPCR analysis indicated differences in relative transcript abundance among these variants. Statistical analysis of fluorescence data demonstrated significant differences among constructs (one-way ANOVA, p < 0.05). Because the reporter assay was based on plasmid expression, the observed differences likely reflect combined contributions from transcription, transcript abundance, RNA stability, and translation rather than translation alone. These findings demonstrate that the SL4 region contributes substantially to reporter gene expression in this experimental system, whereas the remaining stem-loop regions examined exert comparatively modest effects. This study provides additional insight into the functional organization of the SARS-CoV-2 5'UTR and establishes a framework for future investigations aimed at distinguished the transcriptional, post-transcriptional, and translational contributions of individual RNA structural elements.

5' Untranslated Regions↗

PubMed2026

E2F7 promotes lung adenocarcinoma progression by affecting phosphorylation and stabilization of β-catenin.

BACKGROUND: E2F transcription factor 7 (E2F7) has been implicated in the tumorigenesis and progression of multiple cancer types; however, the molecular mechanisms through which E2F7 regulates malignant phenotypes in cancer cells remain largely undefined. In this study, we investigated the biological functions and underlying mechanisms of E2F7 in lung adenocarcinoma (LUAD). METHODS: E2F7 expression in LUAD was analyzed using The Cancer Genome Atlas (TCGA) datasets and further validated in clinical specimens via quantitative real-time polymerase chain reaction (PCR) and immunohistochemistry. The effects of E2F7 on cancer cell self‑renewal and epithelial-mesenchymal transition (EMT) were assessed using sphere formation and Transwell assays, respectively. In vivo tumorigenicity and metastasis were evaluated using xenograft models combined with extreme limiting dilution analysis to assess tumor-initiating capacity. Wnt/β‑catenin pathway activity was measured using T-cell factor optimal promoter luciferase reporter plasmid/far-from optimal promoter luciferase reporter plasmid (TOP/FOP) flash reporter assays. β‑Catenin expression, stability, and ubiquitination were examined via western blotting, cycloheximide chase assays, and ubiquitination assays. Protein-protein interactions among E2F7, β‑catenin, and glycogen synthase kinase 3 beta (GSK3β) were verified through co‑immunoprecipitation (Co‑IP), glutathione S‑transferase (GST) pull‑down, and immunofluorescence assays. Truncated mutants were generated to map the functional binding domains of E2F7. In vitro immunoprecipitation and kinase assays were further performed to confirm that E2F7 regulates GSK3β autophosphorylation and β‑catenin phosphorylation. RESULTS: Bioinformatic analyses revealed that E2F7 was significantly upregulated in LUAD tissues, and elevated E2F7 expression correlated with poor patient prognosis. Functional assays demonstrated that E2F7 promoted LUAD cell self‑renewal and EMT. Mechanistically, cytoplasmic E2F7 directly associated with β‑catenin through its DNA‑binding domain (DBD) and PHA03247 domain. E2F7 modulated β‑catenin phosphorylation at Ser675 and Ser33/37/T41, thereby inhibiting ubiquitin‑mediated degradation and enhancing β‑catenin protein stability. Furthermore, E2F7 interacted with GSK3β and suppressed its autophosphorylation at Tyr216, concomitant with reduced β-catenin phosphorylation at Ser33/37/T41 and its accumulation. CONCLUSION: Collectively, these findings indicate that E2F7 drives LUAD malignant progression through regulation of the GSK3β/β‑catenin signaling axis and stabilization of β‑catenin. This study unveils a novel oncogenic mechanism of E2F7 in LUAD and identifies E2F7 as a promising therapeutic target for clinical intervention in LUAD.

E2F7↗

PubMed2025

Identification of gene targets regulated by the IclR-like regulator SL1344_3500 in Salmonella Typhimurium.

Transcriptional regulation of metabolic operons is important for optimal carbohydrate use and for mitigating the accumulation of toxic intermediates. Here, we characterize SL1344_3500, encoding a putative IclR-like regulator in Salmonella enterica Typhimurium. We present genetic and transcriptional evidence that it regulates the expression of two neighboring operons, one designated here as xynABC, enables utilization of xylonate as a sole carbon source. Furthermore, our findings indicate that SL1344_3500 is important for luminal growth in several mouse models, exerting its effects through the suppression of the xynABC operon. Based on the observation that the ΔSL1344_3500 deletion can be stably complemented in vivo, we developed a plasmid stabilization strategy. This gene complementation approach shows promise for generating stable gene reporters for long-term colonization experiments.IMPORTANCEUnderstanding transcriptional regulation in Salmonella enterica Typhimurium is crucial for revealing how enteric pathogens optimize metabolism to compete with commensals in the gut. SL1344_3500, an IclR-like transcriptional regulator controlling genes linked to sugar acid metabolism, is essential for luminal growth in mouse models through gene suppression and represents a potential target for antimicrobial development. Based on these observations, we developed stable reporter plasmids that use gene complementation of SL1344_3500 to prevent plasmid loss during long-term in vivo studies.

Salmonella typhimurium↗

PubMed2026

Fluorescent reporter assay reveals ribonucleotides promote mismatch correction in vivo.

Ribonucleotides can serve as a strand discrimination signal in reconstituted in vitro biochemical mismatch repair (MMR) assays, but the influence of ribonucleotides on mismatch correction has not been measured directly in vivo. We have developed a fluorescence-based host cell reactivation assay that reports correction of a mismatch in proximity of a site-specifically incorporated ribonucleotide. A ribonucleotide leads to enhanced mismatch correction. While neither inactivation of a single allele nor knockdown of RNaseH2 is sufficient to suppress ribonucleotide directed MMR, a modest but statistically significant impairment for repair of mismatches in the presence of an embedded ribonucleotide is observed in RNaseH2 knockout cell lines. Reporter plasmids with ribonucleotides located in either the 3' or 5' orientation are robustly repaired in MMR-proficient cells but are weakly repaired in MMR-deficient cells, underscoring their utility as effective MMR reporters. Significant ribonucleotide-enhanced mismatch correction was consistently observed in MMR-deficient cells when the ribonucleotide is in the 3' orientation. The presence of a ribonucleotide led to enhanced MMR even in RNaseH2 knockout cells, suggesting that other enzymes may promote ribonucleotide-directed MMR. Loss of RNaseH2 was not sufficient to confer significant resistance to the alkylating agent, temozolomide, in support of a model in which ribonucleotide-directed repair events make minor contributions to the canonical MMR pathway in mammalian cells. We propose a model in which MMR-independent ribonucleotide enhanced correction of mismatches can proceed by ribonucleotide excision repair when the ribonucleotide is in the 5' direction, and proceeds by an unknown mechanism when the ribonucleotide is in the 3' direction.

DNA Mismatch Repair↗

PubMed2005

SUMO modification of the Ets-related transcription factor ERM inhibits its transcriptional activity.

A variety of transcription factors are post-translationally modified by SUMO, a 97-residue ubiquitin-like protein bound covalently to the targeted lysine. Here we describe SUMO modification of the Ets family member ERM at positions 89, 263, 293, and 350. To investigate how SUMO modification affects the function of ERM, Ets-responsive intercellular adhesion molecule 1 (ICAM-1) and E74 reporter plasmids were employed to demonstrate that SUMO modification causes inhibition of ERM-dependent transcription without affecting the subcellular localization, stability, or DNA-binding capacity of the protein. When the adenoviral protein Gam1 or the SUMO protease SENP1 was used to inhibit the SUMO modification pathway, ERM-dependent transcription was de-repressed. These results demonstrate that ERM is subject to SUMO modification and that this post-translational modification causes inhibition of transcription-enhancing activity.

Adenoviridae↗

PubMed2026

Site-specific gene integration by recombinase-mediated cassette exchange in anhydrobiotic Pv11 cells.

Pv11 cells, derived from Polypedilum vanderplanki, uniquely tolerate complete desiccation (anhydrobiosis). Although a CRISPR/Cas9-based precise integration method (CRIS-PITCh) has been developed for Pv11 cells, a CRISPR-free strategy that fixes both the genomic locus and transgene copy number has not yet been established. Here, we implement recombinase-mediated cassette exchange (RMCE) in Pv11 cells and generate master cell lines that retain anhydrobiosis following genetic engineering. We first evaluated the activity of multiple site-specific recombinases in Pv11 cells using a transient two-plasmid reporter assay. Flp, Cre, and Bxb1 recombinases all excised a test cassette and activated a green fluorescent protein (GFP) reporter, whereas phiC31 integrase mediated recombination at the DNA sequence level but did not induce reporter expression under our construct configuration. To enable genomic RMCE, we inserted an FRT/FRT3-landing pad (LP) into a previously identified genomic safe-harbor locus using CRIS-PITCh and isolated clonal master cell lines by single-cell sorting. Using the established master line, Flp-based RMCE achieved site-specific cassette exchange at the LP, producing HaloTag fluorescence and drug resistance upon successful exchange. In addition, the expected post-exchange sequence was confirmed by sequencing. We further established an all-in-one RMCE vector combining the Flp recombinase and donor cassette on a single plasmid. Together, these results demonstrate locus-defined, single-copy transgene integration in anhydrobiotic Pv11 cells via RMCE and provide a standardized, CRISPR-free workflow for routine genetic manipulation in this unique cell line. This workflow facilitates both fundamental research and applied biotechnological applications using desiccation-tolerant cells.

Anhydrobiosis↗

PubMed2010

Human dopamine β-hydroxylase promoter variant alters transcription in chromaffin cells, enzyme secretion, and blood pressure.

BACKGROUND: Dopamine β-hydroxylase (DBH) plays an indispensable role in catecholamine synthesis by converting dopamine into norepinephrine. Here, we characterized a DBH promoter polymorphism (C-2073T; rs1989787; minor allele frequency ~16%) that influences not only gene transcription but also enzyme secretion and blood pressure (BP) in vivo. METHODS: Plasma DBH activity was measured spectrophotometrically. DBH genetic effects on BP were tested in subjects with the most extreme BP values in a large primary care population. Functional effects of promoter variants were studied by site-directed mutagenesis in DBH promoter haplotype/luciferase reporter plasmids transfected into chromaffin cells. Sequence motifs were predicted from position weight matrices, and endogenous transcription factor binding was probed by Chromatin ImmunoPrecipitation (ChIP). RESULTS: The T-allele of common promoter variant C-2073T was contained in a promoter haplotype that associated with plasma DBH activity, a trait also predicted by that variant itself. Promoter haplotypes including C-2073T predicted BP in the population, and the effect was also referable to C-2073T itself. Computationally, C-2073 disrupted a predicted match for transcription factor c-FOS. Site-directed mutagenesis at C-2073T altered not only basal promoter activity, but also transactivation by c-FOS, as well as the chromaffin cell secretory stimuli nicotine or pituitary adenylate cyclase-activating polypeptide (PACAP). Endogenous c-FOS bound to the motif in chromatin. CONCLUSIONS: These results suggest that DBH promoter variant C-2073T is functional in vivo: this promoter variant seems to initiate a cascade of transcriptional and biochemical changes including augmented DBH secretion, eventuating in elevation of basal BP, and hence cardiovascular risk. The observations suggest new strategies for probing the pathophysiology, risk, and treatment of hypertension.

Animals↗

PubMed2025

Remote Regulation by VirB, the Transcriptional Anti-Silencer of Shigella Virulence Genes, Provides Mechanistic Information.

Classical models of bacterial transcription show regulators binding close to promoter elements to exert their effect. However, the scope for long-range regulation exists, especially by nucleoid structuring proteins, like H-NS. Here, long-range regulation by VirB, a transcriptional regulator that alleviates H-NS-mediated silencing of key virulence genes in Shigella species, is explored in vivo to test the limits of long-range regulation and provide further mechanistic insight. VirB-dependent regulation of the well-characterized icsP promoter persists if its cognate site is repositioned 1 kb, 3.3 kb, and even 4.7 kb further upstream than its native position in a plasmid reporter. VirB-dependent regulation diminishes with binding site distance. While increasing cellular VirB pools elevated promoter activity in all constructs with wild-type VirB binding sites, it did not generate a disproportionate increase in promoter activity from remote sites relative to the native site. Since VirB occludes a constitutively active promoter (PT5) when docked adjacent to its -35 element, we next moved the VirB binding site far outside the promoter region. We discovered that VirB still interfered with promoter activity. These findings and those generated from molecular roadblocks engineered around a distally located VirB-binding site are reconciled with the various models of transcriptional regulation by VirB.

Gene Expression Regulation, Bacterial↗

PubMed2026

Functional Variant Discovery Identifies a Novel Genetic Link between SPRY2, Wood Smoke, and Asthma.

As a consequence of climate change and land-use policies, there has been a historic rise in wildfire smoke across the United States and the world. Although the deleterious effects of wildfire smoke and associated air pollution on asthma outcomes are established epidemiologically, genetic risks and molecular mechanisms of how wildfire smoke affects asthma are unknown. This knowledge gap hinders the identification of high-risk individuals and the creation of targeted therapies or recommendations to protect these individuals. We identified 52 genetic risk variants that colocalized with genomic responses to woodsmoke particles (WSPs), a model of wildfire particulate matter, and associated with asthma in the GERA (Genetic Epidemiology Research on Adult Health and Aging) cohort. We used additional filters to prioritize variants for direct testing of allele-dependent transcriptional regulatory function in plasmid reporters. We found that the rs3861144 variant (odds ratioasthma, 1.036) changes SPRY2 responses to WSPs in airway epithelial cells, which are involved in IL-8 secretion, ERK (extracellular signal-related kinase) activation, and mechanical scratch repair in cell culture. These findings provide insights into the molecular pathways through which WSPs may influence asthma risk and propose genetic candidates that warrant further study for their potential as clinical tools for asthma.

Asthma↗

PubMed1979

Cloning and expression of the yeast galactokinase gene in an Escherichia coli plasmid.

This report describes the construction and isolation of a plasmid, derived from pBR322, which carries a BglII restriction fragment of DNA containing the galactokinase gene from Saccharomyces cerevisiae. This was accomplished by the following procedure: (1) Purified galactokinase mRNA, labelled with 125I, was hybridized to BglII digests of yeast DNA employing Southern's filter transfer technique to identify a restriction fragment containing the galactokinase gene. (2) This fragment was partially purified by agarose gel electrophoresis, ligated into the BamHI site of pBR322 and transformed into Escherichia coli to generate a clone bank containing the galactokinase gene. (3) This bank was screened by in situ colony hybridization with galactokinase mRNA resulting in the identification of a plasmid carrying this gene. This plasmid DNA hybridized with the galactokinase mRNA to the same extent in the presence of absence of a large excess of unlabelled mRNA from cells that were not induced for galactokinase synthesis, while the same amount of unlabelled galactose-induced mRNA reduced the hybridization by 95%. When this plasmid was introduced into an E. coli strain deleted for the galactose operon it caused the synthesis of low levels of yeast galactokinase activity.

DNA, Recombinant↗

PubMed2026

Attomolar Detection of HIV-1 With Label-Free RCA-rCRISPR on Smartphone.

HIV remains a major global public health challenge, causing 42.3 million deaths since its discovery in the early 1980s. Despite progress in prevention and treatment, around 60% of people with HIV (PWH) remain undiagnosed in resource-limited regions due to the lack of inexpensive and equipment-free detection methods. Here, we developed a low-cost, robust, and label-free CRISPR-based diagnostic platform for detecting HIV viral load with minimal instrumentation. Our strategy combines rolling circle amplification (RCA) with plasmid reporter-based ratiometric CRISPR (rCRISPR) that enables the detection of HIV RNA down to single-digit aM sensitivity from PWH-derived HIV samples ex vivo. Unlike conventional RCA, which requires fragmentations of long RNA target sequences, our design harnesses the triple functions of the phi29 DNA polymerase (namely exonuclease activity, polymerization, and strand displacement), enabling the detection of the long HIV genome without pre-fragmentation. Cas12a reaction then detected RCA products by converting supercoiled ΦX174 plasmid reporters to relaxed forms. The target concentration was quantified based on the supercoil-to-relaxed plasmid ratio. Further, we constructed an all-in-one smartphone-based minigel electrophoresis device to demonstrate equipment-free HIV viral load testing. Finally, the assay has demonstrated for BRAF point mutation detection, showcasing the robustness of our strategy for broad disease diagnostic applications.

CRISPR↗

PubMed1976

Recombination between bacterial plasmids leading to the formation of plasmid multimers.

We report here the formation of plasmid multimers in E. coli. Multimers are covalently closed, circular molecules composed of tandem repeats of the monomer plasmid. Multimer formation occurs at high frequency in rec+, recB-C-, and recF- hosts. Multimer formation is not detected in recA- hosts and occurs at reduced frequency in recB-C-F- hosts. We conclude that multimer formation is mediated by a single reciprocal recombination event occurring at homologous regions on the two plasmids.

Coliphages↗

PubMed2025

Attomolar Detection of HIV-1 with Label-Free RCA-rCRISPR on Smartphone.

Human Immunodeficiency Virus-1 (HIV) remains a major global public health challenge, having led to over 42.3 million deaths since its discovery in the early 1980s. Despite progress in prevention and treatment, around 60% of people with HIV (PWH) remain undiagnosed in resource-limited regions, disproportionately affecting vulnerable populations and underserved communities across the world. This illustrates the critical need for accessible, accurate, and equipment-free diagnostic tools to enhance detection and thus provide opportunities to curb its spread. Here, we developed a low-cost, robust, and label-free rolling circle amplification (RCA)-rCRISPR diagnostic platform for detecting HIV viral load with minimal instrumentation. Our strategy, combining the integration of RNA-detecting RCA reaction with plasmid reporter-based ratiometric CRISPR (rCRISPR), enables sensitive detection of unprocessed RNA targets without the need for intensive sample pre-treatment. This label-free RCA-rCRISPR diagnostic platform detected HIV RNA down to single-digit aM sensitivity (~3000 copies/mL) from PWH-derived HIV samples ex vivo. Unlike typical RCA, which requires sample fragmentations to break long RNA target sequences, our design harnesses the triple functions of the phi29 DNA polymerase (namely exonuclease activity, polymerization, and strand displacement), enabling the detection of the entire HIV genome without pre-fragmentation. For point-of-care (POC) applications, we constructed an all-in-one smartphone-based minigel electrophoresis device to facilitate equipment-free HIV viral load testing, making it accessible to resource-limited communities. Additionally, the assay has demonstrated the ability for point mutation detection (BRAF mutation in canine urothelial carcinoma), showcasing the robustness of our strategy for broad disease diagnostic applications.

HIV↗

PubMed1978

Construction and properties of chimeric plasmids in Bacillus subtilis.

Antibiotic resistance chimeric plasmids have been constructed by in vitro enzymatic manipulation and introduced into Bacillus subtilis by transformation. The parental plasmids used had been introduced into B. subtilis from Staphylococcus aureus by transformation. Of the seven recombinant plasmids constructed using restriction endonucleases, one was made using EcoRI, another using Hpa II, and five with Xba I (from Xanthomonas badrii), demonstrating the utility of the latter enzyme for molecular cloning experiments. Although all of the recombinant plasmids we have made replicate and express their antibiotic resistance characters, three of them have suffered a loss of DNA, either in vitro or, more likely, in vivo. The deletion event in all cases involved one of the two termini used to join the parental plasmids. The plasmid chimeras reported in this paper should prove useful for the study of plasmid replication, incompatibility, and recombination. In addition, the utility of the B. subtilis system for molecular cloning has been clearly illustrated.

Bacillus subtilis↗

PubMed1976

Compatibility properties of R483, a member of the I plasmid complex.

R483, an I pilus-determining plasmid previously reported as belonging to a distinct incompatibility group Ibeta, proved to be an atypical Ialpha plasmid; in a growing culture, the degree of inhibition of replication of one Ialpha plasmid by the presence of another was not uniform within the Ialpha group.

Colicins↗

PubMed2026

Dissemination of blaKPC-3-harbouring Klebsiella pneumoniae across ST48 and ST628 in multiple healthcare facilities in the Republic of Korea.

Klebsiella pneumoniae carbapenemase-3 (KPC-3) remains rare in South Korea, where KPC-2 is the dominant carbapenemase, making the repeated detection of a concentrated blaKPC-3 signal over five years notable. We performed genomic analyses of blaKPC-3-harbouring K. pneumoniae from a regional healthcare network. Two chromosomally distinct lineages with concordant capsule loci (ST628/KL15 and ST48/KL62) presented multidrug-resistant phenotypes, and the virulence-associated loci were confined to ST48. Single-nucleotide polymorphism (SNP) analyses revealed near-clonal relatedness within lineages, with 0-38 pairwise SNPs among ST628 isolates and 8 SNPs between the two ST48 isolates. Core-genome multilocus sequence typing (cgMLST) supported this structure, as ST628 isolates were assigned to complex type 19149 with 0-7 allelic differences, and ST48 isolates were assigned to complex type 19150 with 5 allelic differences. These patterns support vertical spread via clonal expansion across multiple facilities. Despite substantial chromosomal separation, most isolates carried the same IncFII(K) plasmid backbone and blaKPC-3, and they were nearly indistinguishable from a plasmid previously reported in South Korea. One isolate carried blaKPC-3 on a distinct multireplicon IncFIB(K)/IncFII(K) plasmid, indicating that the signal was not confined to a single plasmid backbone. In both plasmids, blaKPC-3 was embedded within Tn4401b. These findings indicate that a rare blaKPC-3 genotype can persist regionally through sustained clonal dissemination and that cross-lineage linkage is compatible with past horizontal transfer involving a conserved plasmid. These findings underscore the need for subtype-resolved, regionally coordinated genomic surveillance in connected healthcare networks to detect uncommon carbapenemase variants early.

Klebsiella pneumoniae↗

PubMed1978

Fine cleavage map of a small colicin E1 plasmid carrying genes responsible for replication and colicin E1 immunity.

A small plasmid (pAO2, 1 megadalton) carrying genes responsible for replication and colicin E1 immunity has been constructed from colicin E1 plasmid (A. Oka, K. Sugimoto, and M. Takanami, Proc. Mol. Biol. Jpn., p. 113-115, 1976). pAO2 DNA was cleaved into unique fragments with seven restriction endonucleases (R.HaeII,R.HaeIII,R.HapII,R.HhaI,R.AluI,R.HgaI, and R.HinfI). R.HaeII cleaved pAO2 DNA at two sites, R.HaeIII at four sites, R.HapII at nine sites, R.HhaI at eight sites, R-AluI at nine sites, R.HgaI at two sites, and R.HinfI at four sites, respectively. The order of HaeIII fragments of pAO2 was deduced from the physical map of colicin E1 plasmid previously reported (A. Oka and M. Takanami, Nature (London) 264:193-196, 1976). HapII, HhaI, and AluI fragments of pAO2 were assigned by analyzing overlapping sets of fragments arising upon digestion of individual HaeIII fragments with one of R.HapII, R.HhaI, or R.AluI, and upon their reciprocal digestion. The cleavage sites for R.HaeII, R.HgaI, and R.HinfI were localized on HapII, HhaI, and AluI fragments by combined digestion. On the basis of these data and estimates of the size of each fragment, a fine cleavage map of pAO2 was constructed.

Colicins↗