Wolbachia prophage DNA adenine methyltransferase genes in different Drosophila-Wolbachia associations. (Q33900496)

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

title

Wolbachia prophage DNA adenine methyltransferase genes in different Drosophila-Wolbachia associations (English)

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

0 references

0 references

Panagiotis Sapountzis

2

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Henk R. Braig

9

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

10

Kostas Bourtzis

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

author name string

Aggeliki Saridaki

1

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Harriet L Harris

3

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Philip D Batista

4

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Jennifer A Biliske

5

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Harris Pavlikaki

6

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Stefan Oehler

7

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

Charalambos Savakis

8

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

language of work or name

English

0 references

publication date

6 May 2011

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

volume

6

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

issue

5

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

page(s)

e19708

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

Creative Commons Attribution 4.0 International

1 February 2020

copyright license

start time

6 May 2011

1 reference

April 2022 Public Data File from Crossref

copyright status

copyrighted

0 references

cites work

UNIDIRECTIONAL INCOMPATIBILITY BETWEEN POPULATIONS OF DROSOPHILA SIMULANS.

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Genomic analysis and relatedness of P2-like phages of the Burkholderia cepacia complex

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Phage WO of Wolbachia: lambda of the endosymbiont world

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Wolbachia: more than just a bug in insects genitals

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

phyloXML: XML for evolutionary biology and comparative genomics

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Complete WO phage sequences reveal their dynamic evolutionary trajectories and putative functional elements required for integration into the Wolbachia genome

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Extensive genomic diversity of closely related Wolbachia strains

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The mosaic genome structure of the Wolbachia wRi strain infecting Drosophila simulans

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Wolbachia-mediated cytoplasmic incompatibility is associated with impaired histone deposition in the male pronucleus

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Genome evolution of Wolbachia strain wPip from the Culex pipiens group

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Multiple rescue factors within a Wolbachia strain

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

jModelTest: phylogenetic model averaging

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

How many species are infected with Wolbachia?--A statistical analysis of current data

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Dam methyltransferase is required for stable lysogeny of the Shiga toxin (Stx2)-encoding bacteriophage 933W of enterohemorrhagic Escherichia coli O157:H7

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

A DNA methylation ratchet governs progression through a bacterial cell cycle

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

A putative DNA adenine methyltransferase is involved in Yersinia pseudotuberculosis pathogenicity

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

DNA adenine methylation and bacterial pathogenesis

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The tripartite associations between bacteriophage, Wolbachia, and arthropods.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

N6-methyl-adenine: an epigenetic signal for DNA-protein interactions

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

No evidence for bacteriophage WO orf7 correlation with Wolbachia-induced cytoplasmic incompatibility in the Culex pipiens complex (Culicidae: Diptera).

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

A mutation inactivating the methyltransferase gene in avirulent Madrid E strain of Rickettsia prowazekii reverted to wild type in the virulent revertant strain Evir

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Dam methylation: coordinating cellular processes

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The Wolbachia genome of Brugia malayi: endosymbiont evolution within a human pathogenic nematode

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

ProtTest: selection of best-fit models of protein evolution

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Bacteriophage flux in endosymbionts (Wolbachia): infection frequency, lateral transfer, and recombination rates

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Natural Wolbachia infections in the Drosophila yakuba species complex do not induce cytoplasmic incompatibility but fully rescue the wRi modification

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Isolation and characterization of the bacteriophage WO from Wolbachia, an arthropod endosymbiont

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Diversity, distribution and specificity of WO phage infection in Wolbachia of four insect species.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Phylogenomics of the reproductive parasite Wolbachia pipientis wMel: a streamlined genome overrun by mobile genetic elements

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

A Simple, Fast, and Accurate Algorithm to Estimate Large Phylogenies by Maximum Likelihood

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Roles of DNA adenine methylation in regulating bacterial gene expression and virulence

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The CcrM DNA methyltransferase of Agrobacterium tumefaciens is essential, and its activity is cell cycle regulated

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Expression of cytoplasmic incompatibility in Drosophila simulans and its impact on infection frequencies and distribution of Wolbachia pipientis.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Distribution and evolution of bacteriophage WO in Wolbachia, the endosymbiont causing sexual alterations in arthropods

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The putative Drosophila methyltransferase gene dDnmt2 is contained in a transposon-like element and is expressed specifically in ovaries

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The Brucella abortus CcrM DNA methyltransferase is essential for viability, and its overexpression attenuates intracellular replication in murine macrophages

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Drosophila proteins related to vertebrate DNA (5-cytosine) methyltransferases

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Plasmid RK2 ParB protein: purification and nuclease properties.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Wolbachia transfer from Drosophila melanogaster into D. simulans: Host effect and cytoplasmic incompatibility relationships.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Cloning and characterization of a gene encoding the major surface protein of the bacterial endosymbiont Wolbachia pipientis

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Wolbachia, normally a symbiont of Drosophila, can be virulent, causing degeneration and early death

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Escherichia coli OxyR modulation of bacteriophage Mu mom expression in dam+ cells can be attributed to its ability to bind hemimethylated Pmom promoter DNA

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The CcrM DNA methyltransferase is widespread in the alpha subdivision of proteobacteria, and its essential functions are conserved in Rhizobium meliloti and Caulobacter crescentus

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Wolbachia infection and cytoplasmic incompatibility in Drosophila species

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Variability within the Seychelles cytoplasmic incompatibility system in Drosophila simulans

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

A prokaryotic dnaA sequence in Drosophila melanogaster: Wolbachia infection and cytoplasmic incompatibility among laboratory strains

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Wolbachia infections and the expression of cytoplasmic incompatibility in Drosophila sechellia and D. mauritiana

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

A technique for radiolabeling DNA restriction endonuclease fragments to high specific activity

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Cleavage of the bacteriophage P1 packaging site (pac) is regulated by adenine methylation.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

16S rRNA phylogenetic analysis of the bacterial endosymbionts associated with cytoplasmic incompatibility in insects

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

The ultrastructure of the rickettsia-like microorganism Wolbachia pipientis and associated virus-like bodies in the mosquito Culex pipiens

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Bacteriophage WO and virus-like particles in Wolbachia, an endosymbiont of arthropods

5 July 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

A Survey of the bacteriophage WO in the endosymbiotic bacteria Wolbachia

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Tracking factors modulating cytoplasmic incompatibilities in the mosquito Culex pipiens

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Wolbachia distribution and cytoplasmic incompatibility during sperm development: the cyst as the basic cellular unit of CI expression

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Clocks and switches: bacterial gene regulation by DNA adenine methylation.

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Unravelling the Wolbachia evolutionary role: the reprogramming of the host genomic imprinting.

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Naturally-occurring Wolbachia infection in Drosophila simulans that does not cause cytoplasmic incompatibility

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

ISWpi1 from Wolbachia pipientis defines a novel group of insertion sequences within the IS5 family

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Rescuing Wolbachia have been overlooked.

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Wolbachia variability and host effects on crossing type in Culex mosquitoes.

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

. . . and discovered on Mount Kilimanjaro

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Functional test of the influence of Wolbachia genes on cytoplasmic incompatibility expression in Drosophila melanogaster.

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

DNA methylation in Drosophila melanogaster.

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

A Dnmt2-like protein mediates DNA methylation in Drosophila

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Selection and orientation of adjacent genes influences DAM-mediated male sterility in transformed maize

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

Species-wide homogeneity of nuclear ribosomal ITS2 sequences in the spider mite Tetranychus urticae contrasts with extensive mitochondrial COI polymorphism

21 January 2018

1 reference

https://api.crossref.org/works/10.1371%2FJOURNAL.PONE.0019708

2001 Fred Griffith review lecture. Immigration control of DNA in bacteria: self versus non-self.

21 January 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=3089641

Male age, host effects and the weak expression or non-expression of cytoplasmic incompatibility in Drosophila strains infected by maternally transmitted Wolbachia

29 October 2018

1 reference

PubMed

https://pubmed.ncbi.nlm.nih.gov/21573076

inferred from PubMed ID database lookup

12 December 2020

based on heuristic

The ParB protein encoded by the RP4 par region is a Ca(2+)-dependent nuclease linearizing circular DNA substrates

1 reference

PubMed

https://pubmed.ncbi.nlm.nih.gov/21573076

inferred from PubMed ID database lookup

12 December 2020

based on heuristic

Identifiers

DOI

10.1371/JOURNAL.PONE.0019708

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

0 references

release_fbzue4owsbco3hvzgfnntecwwm

1 reference

Fatcat

https://api.fatcat.wiki/v0/release/fbzue4owsbco3hvzgfnntecwwm

mapped directly with Wikidata item

24 November 2022

based on heuristic

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:21573076%20AND%20SRC:MED&resulttype=core&format=json

1 February 2020

PubMed publication ID

21573076

1 reference