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DNA sequences complementary to human 7 SK RNA show structural similarities to the short mobile elements of the mammalian genome 总被引:8,自引:0,他引:8
S Murphy F Altruda E Ullu M Tripodi L Silengo M Melli 《Journal of molecular biology》1984,177(4):575-590
A complementary DNA clone of 7 SK RNA from HeLa cells was used to study the genomic organization of 7 SK sequences in the human genome. Genomic hybridizations and genomic clones show that 7 SK is homologous to a family of disperse repeated sequences most of which lack the 3' end of the 7 SK RNA sequence. Only few of the genomic K sequences are homologous to both 3' and 5' 7 SK probes and presumably include the gene(s) for 7 SK RNA. The sequence of four genomic 7 SK clones confirms that they are in most cases pseudogenes. Although Alu sequences are frequently found near the 3' and 5' end of K DNA, the sequences immediately flanking the pseudogenes are different in all clones studied. However, direct repeats were found flanking directly the K DNA or the K-Alu unit, suggesting that the K sequences alone or in conjunction with Alu DNA might constitute a mobile element. 相似文献
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The number of gene copies for tRNA2Gln in λpsu+2 was determined by genetic and biochemical studies. The transducing phage stimulates the production of the su+2 (amber suppressor) and su°2 glutamine tRNAs and methionine tRNAm. When the su+2 amber suppressor was converted to an ochre suppressor by single-base mutation, the phage stimulated ochre-suppressing tRNA2Gln, instead of the amber-suppressing tRNA2Gln. From the transducing phage carrying the ochre-suppressing allele, strains carrying both ochre and amber suppressors were readily obtainable. These phages stimulated both ochre-suppressing and amber-suppressing tRNA2Gln, but not the non-suppressing form. We conclude that the original transducing phage carries two tRNA2Gln genes, one su+2 and one su°2. The transducing phage carrying two suppressors, ochre and amber, segregates one-gene derivatives that encode only one or the other type of suppressor tRNA. These derivatives apparently arise by unequal recombination involving the two glutamine tRNA genes in the parental phage. This segregation is not accompanied by the loss of the tRNAmMet gene. Based on these results, it is suggested that Escherichia coli normally carries in tandem two identical genes specifying tRNA2Gln at 15 minutes on the bacterial chromosome. su+2 mutants may arise by single-base mutations in the anticodon region of either of these two, leaving the other intact. By double mutations, tRNA2Gln genes could also become ochre suppressors. A tRNAmMet gene is located near, but not between, these two tRNA2Gln genes. 相似文献
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The nucleotide sequence in the central region of the extrachromosomal ribosomal DNA palindrome of Tetrahymena pigmentosa has been determined. The sequence data show that 26 nucleotides at the very center are not palindromic. A segment of 34 base-pairs just outside the non-palindromic region is highly conserved between Tetrahymena pigmentosa and Tetrahymena thermophila, while the rest of the central regions show little sequence homology. 相似文献
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Highly reiterated non-coding sequence in the genome of Plasmodium falciparum is composed of 21 base-pair tandem repeats 总被引:8,自引:0,他引:8
L Aslund L Franzén G Westin T Persson H Wigzell U Pettersson 《Journal of molecular biology》1985,185(3):509-516
Clones containing highly reiterated DNA sequences were isolated from a Plasmodium falciparum genomic library. One clone, Rep2, was selected for further characterization by nucleotide sequence analysis. The results revealed that the insert of this clone is composed of tandemly arranged 21 base-pair imperfect repeats. These repeats are estimated to comprise approximately 1% of the P. falciparum genome and there are 10(4) to 2 X 10(5) copies, depending on the genome size estimate used for calculation. Moreover, the repeats are organized in clusters and do not appear to be transcribed in non-synchronized P. falciparum cultures. 相似文献
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Alan J. Kingsman Robert L. Gimlich Louise Clarke A.Craig Chinault John Carbon 《Journal of molecular biology》1981,145(4):619-632
Two new dispersed repetitive DNA sequences related to the transposable element Tyl have been isolated from the genome of Saccharomyces cerevisiae. One sequence, designated Tyl-17, is present at about six copies per haploid genome, and one copy is located approximately 1000 base-pairs from the LEU2 locus on chromosome III. Tyl-17 is about the same size as Tyl (Cameron et al., 1979) and is flanked by δ sequences, but differs from Tyl by the presence of two large substitutions representing about 50% of the sequence. Tyl and Tyl-17 are found in a ‘head-to-head’ array in at least one cloned region of the yeast genome. Another sequence, designated Tyl-161, is situated about 9000 base-pairs from the PGK locus of chromosome III, and is structurally identical to Tyl except for the presence of a 1200 base-pair insertion near one end of the sequence element. 相似文献
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A specific autonomously replicating sequence (ars2) occurring near the ARG4 locus on chromosome VIII of yeast (Saccharomyces cerevisiae) has been localized on a 100 base-pair region of DNA. The nucleotide sequence of a 1517 bp2 fragment spanning the ars2 region has been determined. The 100 bp ars2 region contains an 18 bp A + T sequence of perfect double symmetry (alphabetic symmetry superimposed on dyad symmetry). A 0.3 kb repetitive sequence (solo delta sequence) and a tRNAGln gene are located within the 1517 bp fragment along with ars2. The 100 bp ars2 region may be located within a divergent delta sequence that is oriented in an inverted and nearly tandem position with respect to the solo delta sequence. 相似文献
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M Clerget 《Journal of molecular biology》1984,178(1):35-46
A 140 base-pair DNA segment situated just upstream of the kanamycin resistance gene of transposon Tn2350, a transposon carried by the plasmid R1, was found to act as an origin of replication and allow autonomous replication of a plasmid composed only of the segment and of the tetracycline resistance gene of pBR322. This segment also promotes site-specific recombination: when cloned in pBR322 it promotes multimer formation in a recA- strain. If two copies are cloned on the same plasmid they promote either deletion or inversion of the intervening region, depending on their orientation relative to each other. DNA gyrase seems to be involved in this process since the inversion rate, in a plasmid carrying sequences in opposite orientations, varies in different nalidixic acid-resistant strains (gyr A mutants) independently isolated. 相似文献
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Characterization by deletion mutagenesis in vitro of the promoter region of ompF, a positively regulated gene of Escherichia coli 总被引:20,自引:0,他引:20
The ompF gene codes for a major outer membrane protein whose expression is positively regulated by the ompR and envZ genes. Two sets of promoter deletions, upstream deletions and downstream deletions, were generated in vitro, and the promoter function was studied by connecting them with the tet genes. One of the hybrid genes thus constructed had a functioning ompF-tet hybrid promoter. The 107 base-pair fragment was found to be functioning as the ompF promoter, 90 nucleotides upstream and 17 nucleotides downstream of the mRNA start site that was also determined in this study. The start site was preceded by a convenient Pribnow box. Although the sequence at the -35 region had a low degree of homology to the consensus sequence, analyses of the hybrid promoter suggested that this region is involved in the promoter function in relation to the Pribnow box. They also indicated that the domain responsible for regulation by the ompR gene is located within the -35 region and its upstream region. 相似文献
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The multicopy plasmid ColE1 specifies a small RNA designated RNA1 that has been implicated in copy number control and incompatibility. We have inserted a 148 base-pair ColE1 DNA fragment containing a promoter-less RNA1 gene into a plasmid vector downstream from the tryptophan promoter of Serratia marcesens. The ColE1 RNA1 produced by this plasmid is not functional in vivo due to the presence of 49 nucleotides appended to the 5′-terminus of the wild-type RNA1 sequence. Deletions of these sequences by Bal3I nuclease in vitro and genetic selection for ColE1 incompatibility function in vivo permitted isolation of a plasmid expressing wild-type ColE1 RNA1 initiated properly from the S. marcesens trp promoter. These experiments demonstrate that RNA1 is sufficient to mediate ColE1 incompatibility in vivo. In addition, several plasmids were isolated that contain altered RNA1 genes. These alterations consist of additions or deletions of sequences at the 5′-terminus of RNA1. Analysis of the ability of these altered RNA1 molecules to express incompatibility in vivo suggests that the 5′-terminal region of RNA1 is crucial for its function. 相似文献
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The Clostridium pasteurianum galactokinase gene was cloned by complementation, of the galK locus, into Escherichia coli. Restriction enzyme analysis subcloning and Tn5 mutagenesis indicated that the gene was located on a 1.8 X 10(3) base-pair ClaI-Sau3A fragment that encoded a polypeptide of approximately 40 Mr. Although the C. pasteurianum and the E. coli galactokinases have similar subunit molecular weights, Southern hybridization analysis indicated no strong homology between their genes. Even though this clone showed a low level of galactokinase expression, the Gal+ phenotype, provided by the clostridial galactokinase, was unstable in E. coli, and the gene was frequently inactivated by the spontaneous acquisition of insertion sequences. A second clone containing this gene on a large restriction fragment was isolated by hybridization. This clone was unable to grow on galactose-containing media due to the overproduction of galactokinase. Comparison of the plasmids from these two clones revealed that the second contained an additional 300 base-pairs located at one end of the galactokinase gene. Appropriate operon fusions with a promoter-less E. coli galactokinase gene indicated that these additional 300 base-pairs had promoter activity in E. coli. The DNA sequence of this region which lies upstream of the C. pasteurianum galactokinase gene was determined and compared with that from several clones producing high, low or undetectable amounts of galactokinase. The reasons for the high and low level expression and for the instability of the C. pasteurianum galactokinase in E. coli are discussed. The presence of the galactokinase suggests that galactose is used in C. pasteurianum through the Leloir pathway via galactose 1-phosphate. 相似文献
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Identification of transfer RNA suppressors in Escherichia coli. I. Amber suppressor su+2, an anticodon mutant of tRNA2Gln. 总被引:3,自引:0,他引:3
In order to isolate the gene for amber suppressor su+2 (SupE) in Escherichia coli, a non-defective su+2-transducing phage lambda was isolated in three steps: first, deletion derivatives of F′su+2 gal (λ) were selected, linking su+2 to the right-hand prophage attachment site, attλPB′; second, these F′-factors were relysogenized by λ and defective transducing phages, λdsu+2, were produced by induction; and third, non-defective λpsu+2 transducing phages were produced by recombination of λdsu+2 isolates with λ. Upon infection by λpsu+2, the production of transferRNAs accepting glutamine and methionine was markedly stimulated. Fingerprint analysis of these tRNAs revealed that they consisted of normal tRNA2Gln, mutant tRNA2Gln and tRNAmMet. The mutant tRNA2Gln carried a singlebase alteration from G to A at the 3′-end of the anticodon. The production of tRNA1Gln was not stimulated by the infection of λpsu+2. We conclude that the wild-type allele of su+2 (SupE) is the structural gene for tRNA2Gln, and the su+2 amber suppressor was derived by a single base mutation, changing the anticodon from CUG to CUA, in one of the multi-copy genes for tRNA2Gln. The fact that λpsu+2 also induces the production of tRNAmMet suggests that this tRNA is encoded in the same chromosomal region of E. coli as is tRNA2Gln. 相似文献
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Genetic and physical analysis of the mitochondrial gene for subunit II of yeast cytochrome c oxidase. 总被引:3,自引:0,他引:3
T D Fox 《Journal of molecular biology》1979,130(1):63-82
The mitochondrial genetic locus oxi 1 contains the structural gene for subunit II of Cytochrome c oxidase. In this study, the oxi 1 locus, or at least a major portion of it, has been localized to a 2·4 kb2 HpaII fragment of mitochondrial DNA, by examining the mtDNA of oxi 1 mutants, and rho? yeast strains that selectively retained in amplified form, this region of the mitochondria) genome. The 2·4 kb fragment is missing from the mtDNA of an oxi 1 locus deletion mutant, but is present in the mtDNAs retained by two rho? strains that genetically recombine with all 16 oxi 1 mutants tested, to produce respiring progeny. Two other rho? strains, that retained different but overlapping portions of the oxi 1 locus as determined genetically, contained mtDNAs consisting of “cloned” segments derived from within the 2·4 kb fragment: these rho? mtDNAs hybridized only to the 2·4 kb HpaII fragment of wild-type mtDNA and could not be cleaved with HpaII. Furthermore, these two rho? mtDNAs were found to correspond to sequences from opposite sides of the 2·4 kb fragment that overlap for 100 to 300 base-pairs near the middle of the fragment. Thus, five oxi 1 mutations that recombine with both of these rho? strains could be further localized to this relatively short region of overlap. One such mutation, of particular interest because it produces an altered form of subunit II, was shown to lie on a 75-base-pair fragment that maps in this region of the overlap. The 75-base-pair fragment from the mutant migrates slightly faster during electrophoresis than the corresponding wild-type fragment. In contrast, the mobility of the fragment from a spontaneous revertant was indistinguishable from wild type. 相似文献
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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. 相似文献