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PubMed2003

Hoppel, a P-like element without introns: a P-element ancestral structure or a retrotranscription derivative?

An in silico search for P-transposable-element-related sequences in the Drosophila melanogaster genome allowed us to detect sequences that are similar to P-element transposases. These sequences are located in the central region of 3.4-kb Hoppel elements, a class II transposon. Polymerase chain reaction (PCR) analysis of the insertional polymorphism revealed that these elements are mobile. The 3.4-kb elements are the longest copies of this family ever found. They contain an open reading frame that is long enough to encode a transposase, suggesting that the 3.4-kb elements are the full-length copies of the Hoppel family. Multiple alignments of several P-element transposases from different species and the Hoppel-element-encoded peptide showed that all of the P-element introns and the 5' region of the transposase are absent from the Hoppel sequence. Sequence analysis combined with reverse transcriptase PCR analysis showed that the 3.4-kb Hoppel elements are intronless. P and Hoppel not only share similar amino acid sequences but also have terminal inverted repeats of the same length (31 bp), and their excision footprints present a similar structure, which suggests that their transposases are functionally very similar. Thus, we propose that the Hoppel element family be included in the P-element superfamily. Two evolutionary scenarios are discussed considering the presence /absence of introns within the P-element superfamily.

Amino Acid Sequence↗

PubMed2005

Occurrence of insertion sequences within the genomes and Tn1546-like elements of glycopeptide-resistant enterococci isolated in Brazil, and identification of a novel element, ISEfa5.

Insertion sequences (IS) occur widely within the Tn1546-like elements responsible for VanA glycopeptide resistance in enterococci from several countries. As such insertions can be used as epidemiological markers and for studying horizontal transfer of gene clusters, we investigated the distribution of IS6770, IS1542, IS1216V, IS1476, and IS1251 elements in 26 VanA Enterococcus faecium and 21 VanA Enterococcus faecalis from Brazil. PCR, using genomic DNA as a template, indicated that most of the isolates contained IS6770 (97%), IS1216V (87%) and IS1476 (72%) elements. IS1251 was also detected, but at a higher frequency in E. faecium (80%) than in E. faecalis (14%). None of the isolates harboured IS1542. Only two of 47 isolates had IS elements within their Tn1546-like elements; one possessed IS1251 between vanS and vanH, as reported in the United States; another possessed a novel IS element, designated ISEfa5, located between vanX and van Y. This novel element was found in the genomic DNA of 25 (96%) E. faecium and II (52%) E. faecalis. In stability studies, no IS-mediated changes were detected in the Tn1546-like elements of 25 vancomycin-resistant enterococci (VRE) monitored over 11 months. These results suggest that the occurrence of IS in Brazilian isolates is similar to that reported in American isolates, but that these elements occur rarely within the vanA gene clusters. As patterns of IS carriage did not correlate with the PFGE type of the VRE, the prevalence of IS elements in genomic DNA of VRE is not a useful epidemiological marker. However, the presence of IS-modified Tn1546-like elements, which appear to be rare in Brazil, could be a useful molecular marker in local epidemiological studies to monitor the evolution and horizontal transmission of VanA elements.

Anti-Bacterial Agents↗

PubMed1995

P-element-induced male recombination can be produced in Drosophila melanogaster by combining end-deficient elements in trans.

Male recombination, not normally present in Drosophila melanogaster, can be produced at high rates when target P elements at homologous sites are combined in the presence of transposase protein. We have produced a set of elements by in situ deletion of a particular insertion and have found elements that have deletions stretching into either end. Elements were tested in pairs to see whether they complement each other in their ability to induce recombination. The combination of elements that are deficient for the same end produces very little recombination, but the combination of a right-end and a left-end element can generate recombination values higher than given by two complete P[CaSpeR] elements at homologous sites. This strongly suggests that "hybrid" P elements, containing ends from two different elements, can be recognized by transposase protein. We have also examined genotypes containing a normal and an end-deficient element and found that they yield reasonably high levels of recombination. We interpret the resultant gametes from such genotypes as showing that the majority of events in this genotype derive from the association of complementary ends from the same element, whereas the complementary ends from elements in trans associate in only a minority of cases.

Animals↗

PubMed1989

[Supplementation of essential trace elements during total parenteral nutrition--effects on trace element-deficient rats].

Thirty-one male SD rats, six weeks old, were fed a trace element-deficient diet for two weeks and then divided into three groups and maintained for 1 week as follows: group A with total parenteral nutrition (TPN) without supplementation of trace elements, group B with TPN supplemented with the following 5 trace elements ... iron, zinc, copper, manganese and iodine, and group C with a diet free of the above five trace elements. Another group of eight rats was fed a diet supplemented with the above five trace elements for three weeks as a control (group D). Feeding or TPN without supplementation of trace elements evoked microcytic hypochromic anemia and significant decreases in iron concentrations in plasma and tissues (groups A and C). Supplementation of trace elements in the TPN solution showed a tendency to cure anemia and a significant increase in the iron concentration in tibia (group B). Decreases in the zinc or copper concentrations in plasma and tissues during TPN without trace elements were prevented by supplementation of trace elements in the TPN solution (group B). The plasma zinc and copper concentrations correlated well with their levels in liver, kidney and tibia. Manganese deficiency was not recognized in this investigation (groups A and C), though supplementation of trace elements in the TPN solution increased tissue manganese concentration (group B). Feeding or TPN without supplementation of trace elements induced decreases in plasma triiodothyronine and thyroxine (groups A and C). Supplementation of trace elements in the TPN solution showed a tendency to increase plasma thyroxine (group B).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

A negative tyrosine aminotransferase gene element that blocks glucocorticoid modulatory element-regulated modulation of glucocorticoid-induced gene expression.

Tyrosine aminotransferase (TAT) is the prototypic steroid-inducible gene. Recently, we have found that the modulation of TAT induction properties is reproduced by a novel cis-acting TAT gene element, the glucocorticoid modulatory element (GME). This GME lies about 1 kb upstream of the glucocorticoid response elements (GREs) of the TAT gene and binds a heterooligomer of two recently defined proteins. We now report the existence of an additional TAT gene element between the GME and the GREs that blocks the action of the GME and thus prevents the left shift in the glucocorticoid dose-response curve caused by the GME. This negative element has the properties of a silencer because its activity is relatively position- and orientation-independent. The interaction appears to be stoichiometric in that the effects of a single negative element can be overcome by a second GME. This negative element also has an intrinsic inhibitory activity in the absence of the GME. The majority of the negative element activity could be elicited by a 56-bp sequence between -3105 and -3050 bp of the TAT gene. Multiple, clustered mutations of this sequence reduced, but did not eliminate, the negative activity. Further efforts to restrict the negative element were unsuccessful, suggesting that multiple sequences are required for full activity. High affinity, sequence-specific binding of a trans-acting factor(s) was observed in gel shift assays. This binding was half-maximally competed by a 4.4-fold excess of nonradioactive probe and was very stable once formed (delta H [symbol: see text] dissoc. = 32 kcal/mol), suggesting that low concentrations of a high affinity binding protein(s) exist in nuclear extracts. Further support for this conclusion came from the observation that cotransfection of a plasmid containing multiple copies of the 56-bp negative element was able to relieve the negation of GME activity in a GME-56-bp-GRE reporter construct. These data directly support the role of a trans-acting factor(s) in binding to the 56-bp negative element and blocking GME activity. Collectively, these data suggest that glucocorticoid induction of TAT gene expression is subject to multiple levels of control by several new cis-acting elements and thus is much more complex than previously appreciated.

Base Sequence↗

PubMed2006

Long-distance RNA-RNA interactions between terminal elements and the same subset of internal elements on the potato virus X genome mediate minus- and plus-strand RNA synthesis.

Potexvirus genomes contain conserved terminal elements that are complementary to multiple internal octanucleotide elements. Both local sequences and structures at the 5' terminus and long-distance interactions between this region and internal elements are important for accumulation of potato virus X (PVX) plus-strand RNA in vivo. In this study, the role of the conserved hexanucleotide motif within SL3 of the 3' NTR and internal conserved octanucleotide elements in minus-strand RNA synthesis was analyzed using both a template-dependent, PVX RNA-dependent RNA polymerase (RdRp) extract and a protoplast replication system. Template analyses in vitro indicated that 3' terminal templates of 850 nucleotides (nt), but not 200 nt, supported efficient, minus-strand RNA synthesis. Mutational analyses of the longer templates indicated that optimal transcription requires the hexanucleotide motif in SL3 within the 3' NTR and the complementary CP octanucleotide element 747 nt upstream. Additional experiments to disrupt interactions between one or more internal conserved elements and the 3' hexanucleotide element showed that long-distance interactions were necessary for minus-strand RNA synthesis both in vitro and in vivo. Additionally, multiple internal octanucleotide elements could serve as pairing partners with the hexanucleotide element in vivo. These cis-acting elements and interactions correlate in several ways to those previously observed for plus-strand RNA accumulation in vivo, suggesting that dynamic interactions between elements at both termini and the same subset of internal octanucleotide elements are required for both minus- and plus-strand RNA synthesis and potentially other aspects of PVX replication.

Base Sequence↗

PubMed1985

Extrachromosomal DNA forms of copia-like transposable elements, F elements and middle repetitive DNA sequences in Drosophila melanogaster. Variation in cultured cells and embryos.

Drosophila melanogaster embryos and cells in culture were screened for the presence of unintegrated covalently closed circular DNA forms that hybridize to copia-like transposable elements, the F element and uncharacterized dispersed middle repetitive DNA elements. Our results indicate that the majority of copia-like elements (including copia, 297, 412, mdg1, mdg3 and gypsy), the F elements, and 9 of 12 middle repetitive DNA elements are present as free DNA forms in cultured cells and embryos. An 18 base-pair inverted repeat has been reported to flank the long direct repeat of mdg3, implying that mdg3 is not an orthodox copia-like element; however, we have sequenced two independently isolated mdg3 clones and shown that the inverted repeat is not part of the element. The relative abundance with which free DNA forms are found varies between the cultured cells used, and between cultured cells and embryos. This variation, which can be up to 20-fold for some elements, does not correlate well with either the amount of element-specific poly(A)+ RNA present per cell or the number of element-specific sequences integrated in the genome.

Animals↗

PubMed1992

The distribution of transposable elements within and between chromosomes in a population of Drosophila melanogaster. II. Inferences on the nature of selection against elements.

Data were collected on the distribution of nine families of transposable elements among a sample of autosomes isolated from a natural population of Drosophila melanogaster, by means of in situ hybridization of biotinylated probes to polytene chromosomes. There is no general tendency for elements to accumulate at the tips of chromosomes. Elements tend to be present in excess of random expectation in the euchromatin proximal to the centromeres of the major autosomes, and on chromosome four. There is considerable heterogeneity between different families in the extent of this excess. The overall abundance of element families is inversely related to the extent to which they accumulate proximally. The level of proximal accumulation for the major autosomes is similar to that on the fourth chromosome, but less than that for the X chromosome. There is an overall deficiency of elements in the mid-section of the X compared with the mid-sections of the major autosomes, with considerable heterogeneity between families. The magnitude of this deficiency is positively related to the extent to which elements accumulate proximally. No such deficiency is seen if the proximal regions of the X and autosomes are compared. There is a small and non-significant excess of elements in third chromosomes carrying inversions. There is some between-year heterogeneity in element abundance. The implications of these findings are discussed, and it is concluded that they generally support the hypothesis that transposable element abundance is regulated primarily by the deleterious fitness consequences of meiotic ectopic exchange between elements. If this is the case, such exchange must be very infrequent in the proximal euchromatin, and the elements detected in population surveys of this kind must be inserted into sites where they have negligible mutational effects on fitness.

Animals↗

PubMed1991

Identification of nucleotide substitutions necessary for trans-activation of mariner transposable elements in Drosophila: analysis of naturally occurring elements.

Six copies of the mariner element from the genomes of Drosophila mauritiana and Drosophila simulans were chosen at random for DNA sequencing and functional analysis and compared with the highly active element Mos1 and the inactive element peach. All elements were 1286 base pairs in length, but among them there were 18 nucleotide differences. As assayed in Drosophila melanogaster, three of the elements were apparently nonfunctional, two were marginally functional, and one had moderate activity that could be greatly increased depending on the position of the element in the genome. Both molecular (site-directed mutagenesis) and evolutionary (cladistic analysis) techniques were used to analyze the functional effects of nucleotide substitutions. The nucleotide sequence of the element is the primary determinant of function, though the activity level of elements is profoundly influenced by position effects. Cladistic analysis of the sequences has identified a T----A transversion at position 1203 (resulting in a Phe----Leu amino acid replacement in the putative transposase) as being primarily responsible for the low activity of the barely functional elements. Use of the sequences from the more distantly related species, Drosophila yakuba and Drosophila teissieri, as outside reference species, indicates that functional mariner elements are ancestral and argues against their origination by a novel mutation or by recombination among nonfunctional elements.

Animals↗

PubMed1990

The region of a Bacteroides conjugal chromosomal tetracycline resistance element which is responsible for production of plasmidlike forms from unlinked chromosomal DNA might also be involved in transfer of the element.

Large (greater than 50 kilobases) conjugal chromosomal tetracycline resistance (Tcr) elements have been found in many human colonic Bacteroides strains. Recently, N. B. Shoemaker and A. A. Salyers (J. Bacteriol, 170:1651-1657, 1988) reported that some of these Tcr elements appeared to mediate production of plasmidlike forms, NBU1 and NBU2, from an unlinked region of the chromosome of Bacteroides uniformis 0061. Production of the plasmidlike forms and the transfer frequency of the Tcr elements were both enhanced by preexposure to tetracycline. Thus it appeared that genes involved in production of plasmidlike forms (Plf activity) might be coregulated with transfer genes and that Plf activity might have a role in transfer of the Tcr elements. By screening subclones of a Tcr element, Tcr Emr DOT, we have shown that the genes necessary for Plf activity on the Tcr element are within a 10-kilobase region adjacent to the Tcr gene. Subclones of this region were then used to construct insertional gene disruptions in a Tcr element, Tcr ERL, which is closely related to the Tcr Emr DOT element. Two of the disruption mutants were Plf-. Both had reduced transfer frequencies, one (omega RDB2) 10(2)-fold lower than that of the wild-type element and the other (omega RDBT) 10(4)-fold lower. omega RDB2 was also deficient in the ability to mobilize coresident plasmids, whereas omega RDBT exhibited nearly wild-type mobilization activity. The phenotypes of the mutants indicate that there are at least two genes necessary for Plf activity and that both may be involved in transfer of the element. The third disruption mutant (omegaRDB1), which expressed Plf constitutively, also had a transfer frequency 10(2) -fold lower than that of the wild-type element and was deficient in mobilization of coresident plasmids. The relationship between Plf genes and transfer, therefore, appears to be a complex one.

Bacteroides↗

PubMed2005

Evidence of P-element-induced sister-chromatid exchange in a ring-X chromosome in Drosophila, with implication for a high rate of formation of hybrid elements.

Activation of a single incomplete P element induces recombination at a rate of approximately 0.5-1% in the male germline of Drosophila. Male recombination rises by an order of magnitude to approximately 20% if homologous P elements are involved. The high rate of recombination suggests the possibility that sister-chromatid exchange (SCE) might be elevated to a similar extent, since homologous P elements must always be present in sister chromatids. This possibility was tested by recombining a single P element onto a ring-X chromosome and using sex-ratio distortion to measure the loss of the ring-X due to SCE in the male germline. The results confirmed a rate of loss comparable to that expected with homologous elements, although the rate of loss was variable. Both SCE and recombination results are consistent with the "hybrid element insertion" model, in which the left and right ends from different elements associate, providing that insertion occurs preferentially in the vicinity of a P-element end. For autosomes, hybrid element formation may thus occur at a much higher rate than the 0.5-1% implied by single element recombination, with only a small minority of hybrid element excision events being resolved by recombination.

Aging↗

PubMed1989

Activation of the serum response element and 12-O-tetradecanoylphorbol-13-acetate response element by the activated c-raf-1 protein in a manner independent of protein kinase C.

Transfection of the cDNA encoding the activated c-raf-1 protein or addition of 12-O-tetradecanoylphorbol-13-acetate (TPA) or dibutyryl cAMP to NIH/3T3 cells activated the c-fos gene enhancer linked to the chloramphenicol acetyltransferase or luciferase reporter gene. Prolonged treatment of NIH/3T3 cells with phorbol 12,13-dibutyrate caused down-regulation of protein kinase C. In these cells, addition of TPA did not stimulate the c-fos gene enhancer any more, but transfection of the c-raf-1 cDNA or addition of dibutyryl cAMP still stimulated the c-fos gene enhancer to the same extent as those induced in the control cells. Transfection of the c-raf-1 cDNA or addition of TPA to NIH/3T3 cells stimulated the serum response element and TPA response element but not the cAMP response element. In contrast, addition of dibutyryl cAMP to NIH/3T3 cells stimulated the cAMP response element but not the serum response element or TPA response element. These results indicate that the activated c-raf-1 protein stimulates the serum response element and TPA response element in a manner independent of protein kinase C and cAMP-dependent protein kinase. Since the c-fos gene enhancer has been shown to contain the serum response element and cAMP response element, it is most likely that the c-raf-1 protein is involved in the regulation of c-fos gene expression through the serum response element.

Animals↗

PubMed1994

[Studies on the components of trace elements and macro elements in hemolymph of Anopheles anthropophagus].

The elements in hemolymph of An. anthropophagus were determined by ICAP. There were 18 kinds of trace elements such as Fe,Zn,Cu,Mn,Cr,Mo,Co,Ni,V,Sr,B,Al,Ba,Zr, Cd,Pb,Ga,Li and 6 kinds of macro elements such as Ca,Mg,K,Na,S,P in the hemolymph of the mosquito. The contents of the macro elements and Fe in hemolymph of newly emerged mosquitoes were significantly higher than those of mosquitoes after taking blood meal, whereas Zn and Al were lower. Comparing elements in hemolymph of An. anthropophagus and An. sinensis, there were 14 kinds of elements in newly emerged mosquitoes with striking significant difference, while there were 13 kinds of elements with striking significant difference in the mosquitoes after taking blood meal. Comparing elements in the hemolymph of An. anthropophagus and Ae. albopictus, there were 13 kinds of elements with striking significant difference in the hemolymph of newly emerged mosquitoes and the mosquitoes after taking blood meal. The results suggested that the components of elements in hemolymph were relevant to the nutritional metabolism and development of mosquitoes, and that mosquitoes of different species and with different sensibilities to malaria parasites also showed difference in the contents of elements in their hemolymph.

Aedes↗

PubMed1998

Transactivation of the human apolipoprotein CII promoter by orphan and ligand-dependent nuclear receptors. The regulatory element CIIC is a thyroid hormone response element.

The regulatory elements CIIC (-159/-116) and CIIB (-102/-81) of the apolipoprotein CII (apoCII) promoter have distinct specificities for orphan nuclear receptors (Vorgia, P., Zannis, V. I., and Kardassis, D. (1998) J. Biol. Chem. 273, 4188-4199). In this communication we investigated the contribution of ligand-dependent and orphan nuclear receptors on the transcriptional regulation of the human apoCII gene. It was found that element CIIC in addition to ARP-1 and EAR-2 binds RXRalpha/T3Rbeta heterodimers strongly, whereas element CIIB binds hepatic nuclear factor 4 (HNF-4) exclusively. Binding is abolished by mutations that alter the HRE binding motifs. Transient cotransfection experiments showed that in the presence of T3, RXRalpha/T3Rbeta heterodimers transactivated the -205/+18 apoCII promoter 1.6- and 11-fold in HepG2 and COS-1 respectively. No transactivation was observed in the presence of 9-cis-retinoic acid. Transactivation requires the regulatory element CIIC, suggesting that this element contains a thyroid hormone response element. HNF-4 did not affect the apoCII promoter activity in HepG2 cells. However, mutations in the HNF-4 binding site on element CIIB and inhibition of HNF-4 synthesis in HepG2 cells by antisense HNF-4 constructs decreased the apoCII promoter activity to 25-40% of the control, indicating that HNF-4 is a positive regulator of the apoCII gene. ARP-1 repressed the -205/+18 but not the -104/+18 apoCII promoter activity in HepG2 cells, indicating that the repression depends on the regulatory element CIIC. In contrast, combination of ARP-1 and HNF-4 transactivated different apoCII promoter segments as well as a minimal adenovirus major late promoter driven by the regulatory element CIIB. Mutagenesis or deletion of elements CIIB or CIIC established that the observed transactivation requires DNA binding of one of the two factors and may result from HNF-4-ARP-1 interactions that elicit the transactivation functions of HNF-4. The combined data indicate that RXRalpha/T3Rbeta in the presence of T3 and HNF-4 can upregulate the apoCII promoter activity by binding to the regulatory elements CIIC and CIIB, respectively. In addition, ARP-1 can either have inhibitory or stimulatory effects on the apoCII promoter activity via different mechanisms.

Animals↗

PubMed2005

Molecular tools to detect the IncJ elements: a family of integrating, antibiotic resistant mobile genetic elements.

The IncJ group of enterobacterial mobile genetic elements, which include R391, R392, R705, R997 and pMERPH, have been shown to be site-specific integrating elements encoding variable antibiotic and heavy metal resistance genes. They insert into a specific 17-bp site located in the prfC gene, encoding peptide release factor 3, in Escherichia coli and other hosts. A key feature of known IncJ elements is the presence of a site-specific recombination module consisting of an attachment site on the element and an integrase-encoding gene of the tyrosine recombinase class, which promotes integration between the attachment site on the element and a similar site on the host chromosome. We have cloned and sequenced the integrases from a number of known IncJ elements and designed PCR primers for specific amplification of this gene. Using conserved regions of enterobacterial prfC genes upstream and downstream of the insertion site, and conserved sequences at the ends of the integrated IncJ elements, we have designed specific primers to amplify across the integrated IncJ attL and attR junction fragments. Alignment of over 30 enterobacterial prfC-like genes indicates that the primers designed to amplify attR junction would amplify IncJ element: host junctions from a wide variety of hosts. The IncJ elements have been shown to sensitise recA(+)E. coli K12 strains to UV irradiation. A simple and rapid procedure for demonstrating this effect is described. These tools should enable the rapid detection of such elements in clinical and environmental settings.

Attachment Sites, Microbiological↗

PubMed1987

Evolution of P transposable elements: sequences of Drosophila nebulosa P elements.

P elements have been cloned and sequenced from Drosophila nebulosa. Their sequences have diverged less than 6% from P elements of Drosophila melanogaster. However D. nebulosa P elements have nucleotide changes that close all four open reading frames found in the D. melanogaster P element. Microinjection experiments show that D. nebulosa P elements cannot provide transposase function for D. melanogaster P elements, nor are D. nebulosa P elements mobilized by the transposase provided by a D. melanogaster P factor. Three D. nebulosa P elements appear to have integrated into the same position of a complex, centromeric repeated sequence. Comparison of nucleotide sequences suggests that D. nebulosa P elements have diverged upon different pathways from a common ancestor that was 99% homologous to the P elements of D. melanogaster.

Base Sequence↗

PubMed1989

E1A-induced enhancer activity of the poly(dG-dT).poly(dA-dC) element (GT element) and interactions with a GT-specific nuclear factor.

The alternating sequence poly(dG-dT).poly(dA-dC) is a highly repeated sequence in the eucaryotic genome. We have examined the effect of trans-acting early viral proteins on the ability of the GT element to stimulate transcription of the adenovirus major late promoter (MLP). We find that the GT element alone does not activate expression from the MLP in either the presence or absence of another enhancer element. However, in the presence of the E1A gene products of either adenovirus type 5 or 2, the GT element activated expression from the MLP. The stimulatory activity of the GT element in the presence of E1A had the properties of an enhancer element, and the trans-activating effect on the GT element was additive in conjunction with the E1A-responsive BK virus enhancer. We also have demonstrated that a specific nuclear factor(s) binds to the GT element. However, the E1A protein(s) do not affect the initial factor interaction(s) with the GT element. Overall, our data demonstrate that trans modulation of promoter activity can be mediated through the GT element.

Adenovirus Early Proteins↗

PubMed1987

Repressor of P elements in Drosophila melanogaster: Cytotype determination by a defective P element carrying only open reading frames 0 through 2.

The P element is a type of transposable element in Drosophila melanogaster. Characteristics of the syndrome of "hybrid dysgenesis" are due to transposition of P elements, and the molecular mechanism for regulation of this transposition has been unknown. In this study a Q strain (which carries only defective P elements in its genome but still is able to repress the transposition of complete P elements although defective in transposase activity) was used to determine the structure of the P element with this repressor (or P cytotype-determining) domain. Examination of the cytotype and structure of the P elements of particular strains with reduced copy number of P elements showed that the P element with a repressor domain was defective, being deleted between bases 1991 and 2448. This region corresponds to most of the third intron [between open reading frame (ORF) 2 and ORF 3] as well as half the ORF 3 of an intact P element. Therefore ORF 3 was deemed to be unnecessary for repressor production.

Journal Article↗