In vivo restriction. Sequence and structure of endonuclease II-dependent cleavage sites in bacteriophage T4 DNA.

Endonuclease II of bacteriophage T4 is required for in vivo restriction of cytosine-containing DNA from its host, Escherichia coli, (as well as from phage mutants lacking cytosine modification), normally the first step in the reutilization of host DNA nucleotides for synthesis of phage DNA in infected cells. The phage cytosine-DNA is fragmented incompletely to yield genetically defined fragments. This restriction is different from that of type I, II, or III restriction enzymes. We have located seven major endonuclease II-dependent restriction sites in the T4 genome, of which three were analyzed in detail; in addition, abundant sites were cleaved in less than or equal to 5% of all molecules. Sites I, II, and III shared the sequence 5'-CCGNNTTGGC-3' and were cleaved in about 25% (I and III) and 65% (II) of all molecules, predominantly staggered around the first or second of the central unspecified base pairs to yield fragments with one 5' base. The less frequently cleaved sites I and III deviated from site II in predicted helical structure when viewed from the consensus strand, and in sequence when viewed from the opposite strand. Thus, interaction with a particular helical structure as well as recognition of the bases in DNA appears important for efficient cleavage.     

Degradation of Escherichia coli Chromosome After Infection by Bacteriophage T4: Role of Bacteriophage Gene D2a

Mutations in the D2a gene of bacteriophage T4 have recently been shown to result in the stabilization of cytosine-containing phage deoxyribonucleic acid (DNA) made after infection by phage gene 56 (deoxycytidine triphosphatase) mutants. In the experiments reported here, we investigate the role of the D2a gene in the degradation of the host chromosome. We find that if T4 endonuclease II, a product of the phage gene denA, is active, host chromosome degradation appears normal, regardless of the presence of the D2a gene product. However, if T4 endonuclease II is absent, a small amount of host chromosome degradation occurs, but only if the D2a product is present. These results are interpreted in terms of the hypothesis that D2a controls a nuclease which degrades cytosine-containing DNA. Neither D2a nor denA mutations affect the shut-off of host DNA synthesis.     

Physical mapping of bacteriophage T4

Summary The 134 positions of the cleavage sites of the restriction endonucleases XbaI, HaeII and EcoRI were determined for a cytosine-containing DNA of bacteriophage T4. This physical map was aligned with the genetic map. The T4 early regions were further identified by hybridization of RNA synthesized in vitro to the restriction fragments and two promoter regions were localized by filter binding tests and R-loop analysis.     

The BAM H1 Restriction Site in the Bacteriophage T4 Chromosome Is Located in or near Gene 8

Bacteriophage T4 cytosine-containing DNA is cleaved at a single site by the restriction endonuclease, Bam H1. The site lies within the late region of the T4 genome, close to, or within, gene 8, one of the structural genes of the phage particle baseplate.     

Physical map of the bacteriophage T5 genome based on the cleavage products of the restriction endonucleases SalI, SmaI, BamI, and HpaI.

A physical map of the bacteriophage T5 genome was constructed by ordering the fragments produced by cleavage of T5 DNA with the restriction endonucleases SalI (4 fragments), SmaI (4 fragments), BamI (5 fragments), and HpaI (28 fragments). The following techniques were used to order the fragments. (i) Digestion of DNA from T5 heat-stable deletion mutants was used to identify fragments located in the deletable region. (ii) Fragments near the ends of the T5 DNA molecule were located by treating T5 DNA with lambda exonuclease before restriction endonuclease cleavage. (iii) Fragments spanning other restriction endonuclease cleavage sites were identified by combined digestion of T5 DNA with two restriction endonucleases. (iv) The general location of some fragments was determined by isolating individual restriction fragments from agarose gels and redigesting the isolated fragments with a second restriction enzyme. (v) Treatment of restriction digests with lambda exonuclease before digestion with a second restriction enzyme was used to identify fragments near, but not spanning, restriction cleavage sites. (vi) Exonucleases III treatment of T5 DNA before restriction endonuclease cleavage was used to locate fragments spanning or near the natural T5 single-chain interruptions. (vii) Analysis of the products of incomplete restriction endonuclease cleavage was used to identify adjacent fragments.     

Cloning and Physical Mapping of an Early Region of the Bacteriophage T4 Genome

We have cloned DNA restriction fragments from the largely nonessential region of bacteriophage T4 located between genes 39 and 56. The cloned DNA fragments were used to construct a precise map of the sites in this region recognized by eight restriction endonucleases. This restriction map allowed us to compare the cytosine-containing T4 DNA used for cloning with the hydroxymethylcytosine-containing DNA of wild-type T4; there were no detectable rearrangements in the region tested. We were also able to determine the physical locations of several deletion end points and of several genes.     

Physical mapping of the restriction fragments obtained from bacteriophage T4 dC-DNA with the restriction endonucleases SmaI, KpnI and BglII.

Summary The cytosine-containing DNA of a mutant of bacteriophage T4 was digested with restriction endonucleases SmaI, KpnI and BglII producing 5, 7 and 13 fragments respectively. Complete physical maps of the T4 genome were constructed with the enzymes SmaI and KpnI and an almost complete map with the enzyme BglII.     

Bacteriophage T4 Endonucleases II and Iv, Oppositely Affected by Dcmp Hydroxymethylase Activity, Have Different Roles in the Degradation and in the RNA Polymerase-Dependent Replication of T4 Cytosine-Containing DNA

Bacteriophage T4 mutants defective in gene 56 (dCTPase) synthesize DNA where cytosine (Cyt) partially or completely replaces hydroxymethylcytosine (HmCyt). This Cyt-DNA is degraded in vivo by T4 endonucleases II and IV, and by the exonuclease coded or controlled by genes 46 and 47.-Our results demonstrate that T4 endonuclease II is the principal enzyme initiating degradation of T4 Cyt-DNA. The activity of endonuclease IV, but not that of endonuclease II, was stimulated in the presence of a wild-type dCMP hydroxymethylase, also when no HmCyt was incorporated into phage DNA, suggesting the possibility of direct endonuclease IV-dCMP hydroxymethylase interactions. Endonuclease II activity, on the other hand, was almost completely inhibited in the presence of very small amounts of HmCyt (3-9% of total Cyt + HmCyt) in the DNA. Possible mechanisms for this inhibition are discussed.-The E. coli RNA polymerase modified by the products of T4 genes 33 and 55 was capable of initiating DNA synthesis on a Cyt-DNA template, although it probably cannot do so on an HmCyt template. In the presence of an active endonuclease IV, Cyt-DNA synthesis was arrested 10-30 min after infection, probably due to damage to the template. Cyt-DNA synthesis dependent on the unmodified (33-55-) RNA polymerase was less sensitive to endonuclease IV action.     

Isolation of Bacteriophage T4 Mutants Defective in the Ability to Degrade Host Deoxyribonucleic Acid

A method was devised for identifying nonlethal mutants of T4 bacteriophage which lack the capacity to induce degradation of the deoxyribonucleic acid (DNA) of their host, Escherichia coli. If a culture is infected in a medium containing hydroxyurea (HU), a compound that blocks de novo deoxyribonucleotide biosynthesis by interacting with ribonucleotide reductase, mutant phage that cannot establish the alternate pathway of deoxyribonucleotide production from bacterial DNA will fail to produce progeny. The progeny of 100 phages that survived heavy mutagenesis with hydroxylamine were tested for their ability to multiply in the presence of HU. Four of the cultures lacked this capacity. Cells infected with one of these mutants, designated T4nd28, accumulated double-stranded fragments of host DNA with a molecular weight of approximately 2 x 10(8) daltons. This mutant failed to induce T4 endonuclease II, an enzyme known to produce single-strand breaks in double-stranded cytosine-containing DNA. The properties of nd28 give strong support to an earlier suggestion that T4 endonuclease II participates in host DNA degradation. The nd28 mutation mapped between T4 genes 32 and 63 and was very close to the latter gene. It is, thus, in the region of the T4 map that is occupied by genes for a number of other enzymes, including deoxycytidylate deaminase, thymidylate synthetase, dihydrofolate reductase, and ribonucleotide reductase, that are nonessential to phage production in rich media.     

Isolation and characterisation of DraI, a type II restriction endonuclease recognising a sequence containing only A:T basepairs, and inhibition of its activity by uv irradiation of substrate DNA

A type II restriction endonuclease, DraI, isolated from Deinococcus radiophilus ATCC 27603 recognises the palindromic hexanucleotide sequence (formula; see text) and cleaves it, as indicated by the arrows, to produce blunt-ended fragments. The yield of enzyme is 100 to 1000 times that of the only other known type II restriction endonuclease that recognises a sequence composed solely of A:T basepairs, the isoschizomer AhaIII (1). Ultraviolet irradiation of the DNA substrate at relatively low doses inhibits the activity of DraI by "protecting" the recognition sequence and this may be exploited to give control of partial digestion of DNA by DraI.     

Simian virus 40 DNA replication: characterization of gaps in the termination region.

A class of precursor DNA (pDNA) II molecules has been identified as the immediate precursor of simian virus 40 DNA I. A pDNA II molecule contains a strand of newly synthesized DNA with an interruption located in the region where DNA synthesis terminates (4). These pDNA II molecules have been isolated and further characterized. They are converted to covalently closed structures (simian virus 40 DNA I) only when they are treated in vitro with both T4 DNA polymerase and Escherichia coli ligase. After in vitro repair of pDNA II with T4 DNA polymerase and nucleoside triphosphates, approximately 7 mol of alpha-[32P]dATP is incorporated per mol of DNA II. Alkaline sucrose analysis of these gap-filled molecules, after they have been cleaved with Eco RI restriction endonuclease, has demonstrated that gaps are specifically located in the termination region. alpha-[32P]dATP is incorporated equally into the two labeled products that are generated by RI cleavage of these molecules. This indicates the presence of gaps in both the newly synthesized plus the minus strands. Electrophoretic analysis of the gap-filled molecules, after they have been cleaved with endonuclease Hind, has shown that gaps are localized in Hind fragments G and B and to a minor degree in fragment J. pDNA II molecules have the following properties. There is a gap in the newly synthesized linear DNA strand contained in the pDNA II molecule. Nicked pDNA II molecules cannot be detected. The two molecules that arise by segregation contain gaps in both of the complementary strands. Based on the amount of alpha-[32P]dATP incorporated and the rate of exonuclease III digestion of gap-filled molecules, it is estimated that the size of the gaps is between 22 and 73 nucleotides. Models for termination of DNA synthesis are proposed based on these findings.     

Plasmids of the cyanobacterium Synechocystis 6701

Abstract Plasmids were obtained from Synechocystis 6701 using a lysis method that employed a hemicellulase digestion procedure. Eight major bands were observed in the initial preparation. Four of the smaller plasmids were isolated using preparative agarose electrophoresis gels and identified by restriction endonuclease analysis. Chromosomal DNA was screened with 15 restriction enzymes and 6 ( Eco RI, Sst I, Hpa I, Bst EII, Acc I, and Bgl II) were effective. Analysis of DNA fragments from plasmids pSCY 1–4 indicated that each plasmid was unique and that their approximate sizes were 5, 7.5, 13.5 and 15 kb, respectively. Digestion of pSCY 1 and pSCY 4 with Bgl II produced DNA fragments that may be used to construct a conjugation vector for this unicellular cyanobacterium.     

DNA polymorphism in the 5′ flanking region of the human carbonic anhydrase II gene on chromosome 8

Summary A restriction-fragment-length polymorphism (RFLP) is described which is associated with the human carbonic anhydrase II gene (CA2) that codes for one of the three genetically distinct carbonic anhydrase isozymes, CA I, CA II, and CA III. The isolated DNA was cleaved with several restriction enzymes and subjected to Southern blot hybridization analysis using a DNA probe containing the 5 end of the human CA II gene. A two allele RFLP which was detected with the restriction endonuclease, Taq I, is expressed phenotypically on Southern blots as either a 5.4 kilobase (kb) fragment or as 4.0 and 1.4 kb fragments. These fragments result from the presence or absence of a Taq I recognition site in the 5 flanking region approximately 1.0kb from the initiation codon of the CA II gene. Segregation analysis showed that the alleles are inherited in a Mendelian fashion, with a frequency of 50%.     

Site-specific recognition of bacteriophage T4 DNA by T4 type II DNA topoisomerase and Escherichia coli DNA gyrase

The site specificity of bacteriophage T4-induced type II DNA topoisomerase action on double-stranded DNA has been explored by studying the sites where DNA cleavages are induced by the enzyme. Oxolinic acid addition increases the frequency at which phi X174 duplex DNA is cut by the enzyme by about 100-fold, to the point where nearly every topoisomerase molecule causes a double-stranded DNA cleavage event. The effect of oxolinic acid on the enzyme is very similar to its effect on another type II DNA topoisomerase, the Escherichia coli DNA gyrase. A filter-binding method was developed that allows efficient purification of topoisomerase-cleaved DNA fragments by selecting for the covalent attachment of this DNA to the enzyme. Using this method, T4 topoisomerase recognition of mutant cytosine-containing T4 DNA was found to be relatively nonspecific, whereas quite specific recognition sites were observed on native T4 DNA, which contains glucosylated hydroxymethylcytosine residues. The increased specificity of native T4 DNA recognition seems to be due entirely to the glucose modification. In contrast, E. coli DNA gyrase shows a high level of specificity for both the mutant cytosine-containing DNA and native T4 DNA, recognizing about five strong cleavage sites on both substrates. An unexpected feature of DNA recognition by the T4 topoisomerase is that the addition of the cofactor ATP strongly stimulates the topoisomerase-induced cleavage of native T4 DNA, but has only a slight effect on cleavage of cytosine-containing T4 DNA.     

Pulsed Field Gel Electrophoresis Analysis of Borrelia burgdorferi Sensu Lato Isolated in Japan and Taxonomic Implications with Lyme Disease Spirochetes

Genomic DNAs of Borrelia burgdorferi sensu lato isolates obtained in Japan sharing different rRNA gene ribotypes were digested with rare-cutter restriction endonucleases and the fragments obtained were separated by pulsed field gel electrophoresis (PFGE). The sizes of large restriction cleavage bands with MluI endonuclease were quite similar among isolates in each ribotype group. On the other hand, the PFGE profiles obtained with the other enzymes (NruI, Sal I or SplI) were rather divergent, and Japanese isolates were distinguishable from the United States and European isolates. The Japanese isolates classified as ribotypes group II (Borrelia garinii) and III (B. afzelii) showed different PFGE patterns from that of European isolates. The isolates grouped into ribotype IV revealed distinctively different PFGE profiles. These results indicate that the Japanese isolates may be genetically divergent and distinct from the United States and European isolates.     

Cleavage map of the simian-virus-40 genome by the restriction endonuclease III of Haemopholus aegyptius.

Enzymic digestion of Simian virus 40 (SV40) DNA with Haemophilus aegyptius restriction endonuclease Hae III results in 10 major and eight minor fragments. These were resolved by electrophoresis on graduated polyacrylamide slab gels. All fragments have been characterized with respect to the size relative to the Haemophilus influenzae Rd fragments (Hind). They were ordered on the SV40 DNA map by means of overlap analysis of the double cleavage products derived from sequential digestion of Hind fragments with Hae III endonuclease and Hae fragments with Hind II + III enzyme, as well as by other reciprocal cleavage experiments, including those involving Haemophilus para-influenzae fragments. In this way the 18 Hae III cleavage sites and the 13 Hind sites have been localized on the circular SV40 DNA map.