(Q34002298)

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

title

Characterization of pic, a secreted protease of Shigella flexneri and enteroaggregative Escherichia coli (English)

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

0 references

1 reference

5

J P Nataro

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

author name string

I R Henderson

1

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

J Czeczulin

2

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

C Eslava

3

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

F Noriega

4

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

language of work or name

English

0 references

publication date

1 November 1999

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

published in

Infection and Immunity

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

volume

67

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

issue

11

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

page(s)

5587-5596

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

Phylogenetic analysis of enteroaggregative and diffusely adherent Escherichia coli.

1 November 2019

cites work

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Identification of a new Escherichia coli She haemolysin homolog in avian E. coli

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Extracellular cysteine protease produced by Streptococcus pyogenes participates in the pathogenesis of invasive skin infection and dissemination in mice

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Regulation of protease expression in Porphyromonas gingivalis.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Shigella and enteroinvasive Escherichia coli strains are derived from distinct ancestral strains of E. coli

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

The great escape: structure and function of the autotransporter proteins

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Molecular and cellular mechanisms of invasion of the intestinal barrier by enteric pathogens. The paradigm of Shigella

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Characterization of BrkA expression in Bordetella bronchiseptica.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Molecular evolution of a pathogenicity island from 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=96930

Pet, an autotransporter enterotoxin from enteroaggregative Escherichia coli.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

In vitro effects of a high-molecular-weight heat-labile enterotoxin from enteroaggregative Escherichia coli.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Phenotypic effect of isogenic uspA1 and uspA2 mutations on Moraxella catarrhalis 035E.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Enteroaggregative Escherichia coli

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Enteroaggregative, Shiga toxin-producing Escherichia coli O111:H2 associated with an outbreak of hemolytic-uremic syndrome

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Structural determinants of processing and secretion of the Haemophilus influenzae hap protein

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Use of a novel approach, termed island probing, identifies the Shigella flexneri she pathogenicity island which encodes a homolog of the immunoglobulin A protease-like family of proteins.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Aggregative adherence fimbria II, a second fimbrial antigen mediating aggregative adherence in enteroaggregative Escherichia coli.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Laboratory investigation of enteroaggregative Escherichia coli O untypeable:H10 associated with a massive outbreak of gastrointestinal illness

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Multidrug-resistant enteroaggregative Escherichia coli associated with persistent diarrhea in Kenyan children

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

An epidemic of diarrhoea in south India caused by enteroaggregative Escherichia coli.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Evolutionary relationships among pathogenic and nonpathogenic Escherichia coli strains inferred from multilocus enzyme electrophoresis and mdh sequence studies

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

EspP, a novel extracellular serine protease of enterohaemorrhagic Escherichia coli O157:H7 cleaves human coagulation factor V.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Effect of shigella enterotoxin 1 (ShET1) on rabbit intestine in vitro and in vivo

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Characterization of EspC, a 110-kilodalton protein secreted by enteropathogenic Escherichia coli which is homologous to members of the immunoglobulin A protease-like family of secreted proteins

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Evidence for degradation of gastrointestinal mucin by Candida albicans secretory aspartyl proteinase

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Bacterial entry into epithelial cells: the paradigm of Shigella

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Enteroaggregative Escherichia coli associated with an outbreak of diarrhoea in a neonatal nursery ward

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Invasion and the pathogenesis of Shigella infections

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Staphylococcus aureus binding to human nasal mucin.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Enteroaggregative Escherichia coli heat-stable enterotoxin 1 represents another subfamily of E. coli heat-stable toxin

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

New outer membrane-associated protease of Escherichia coli K-12.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Isolation and characterization of a gene involved in hemagglutination by an avian pathogenic Escherichia coli 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=96930

Diarrhoeal disease: current concepts and future challenges. Enteroadherent Escherichia coli: a heterogeneous group of E. coli implicated as diarrhoeal pathogens

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Cloning and sequencing of a Bordetella pertussis serum resistance locus.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Sequence variation in Shigella sonnei (Sonnei), a pathogenic clone of Escherichia coli, over four continents and 41 years

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

A Haemophilus influenzae IgA protease-like protein promotes intimate interaction with human epithelial cells

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Signal peptides: exquisitely designed transport promoters

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

A plasmid-encoded regulatory region activates chromosomal eaeA expression in enteropathogenic Escherichia coli.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Role of chemotaxis in the association of motile bacteria with intestinal mucosa: in vitro studies

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

A simple method for displaying the hydropathic character of a protein

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Studies on transformation of Escherichia coli with plasmids

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Vibrio cholerae hemagglutinin/lectin/protease hydrolyzes fibronectin and ovomucin: F. M. Burnet revisited

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Degradation of intestinal glycoproteins by pathogenic Shigella flexneri

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Cleavage of Structural Proteins during the Assembly of the Head of Bacteriophage T4

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

A complementation analysis of the restriction and modification of DNA in Escherichia coli

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

A two-year study of enteric infections associated with diarrhoeal diseases in children in urban Somalia

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Inhibition of attachment of Escherichia coli RDEC-1 to intestinal microvillus membranes by rabbit ileal mucus and mucin in vitro

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Induction of hepatitis A virus-neutralizing antibody by a virus-specific synthetic peptide

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Purification and N-terminal sequence of the alpha subunit of antigen 43, a unique protein complex associated with the outer membrane of Escherichia coli

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Cloning and expression of an adhesin (AIDA-I) involved in diffuse adherence of enteropathogenic Escherichia coli

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Characterization of degP, a gene required for proteolysis in the cell envelope and essential for growth of Escherichia coli at high temperature

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Transposition in Shigella dysenteriae: isolation and analysis of IS911, a new member of the IS3 group of insertion sequences

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Complete sequence of IS629

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Localization of the cleavage site specificity determinant of Haemophilus influenzae immunoglobulin A1 protease genes

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Characterization of binding of Escherichia coli strains which are enteropathogens to small-bowel mucin

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Differences in blood group B-specific mucinase activity between virulent and avirulent Shigella flexneri 2a 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=96930

Epidemiologic patterns of acute diarrhea and endemic Shigella infections in children in a poor periurban setting in Santiago, Chile

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Identification of a protein required for disulfide bond formation in vivo

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Crystal structures explain functional properties of two E. coli porins

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

A Colorimetric Assay for Glycoproteins Based on the Periodic Acid/Schiff Stain

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Construction and characterization of amplifiable multicopy DNA cloning vehicles derived from the P15A cryptic miniplasmid

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Characterization of a hemoglobin protease secreted by the pathogenic Escherichia coli strain EB1.

5 July 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

What happens to bacterial pathogens in vivo?

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Enteroaggregative Escherichia coll and outbreaks of gastroenteritis in UK.

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Rectal histopathology in endemic Shigella and Salmonella diarrhea.

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Characterization of IS1203, an insertion sequence in Escherichia coli O111:H-.

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Heterogeneity of enteroaggregative Escherichia coli virulence demonstrated in volunteers.

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Prevalence of Shigella Enterotoxin 1 among Shigella Clinical Isolates of Diverse Serotypes

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

SepA, the major extracellular protein of Shigella flexneri: autonomous secretion and involvement in tissue invasion

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Isolation and characterization of the native glycoprotein from pig small-intestinal mucus

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Association of Escherichia coli HEp-2 adherence patterns with type and duration of diarrhoea.

29 October 2018

1 reference

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=96930

Detection of complement C3 and factor B gene expression in normal colorectal mucosa, adenomas and carcinomas

29 October 2018

1 reference

12 December 2020

Binding of Shigella to rat and human intestinal mucin

1 reference

12 December 2020

Bacterial adhesion to and penetration of intestinal mucus in vitro

1 reference

12 December 2020

A novel cysteine protease in Entamoeba histolytica

1 reference

12 December 2020

The response of man to virulent Shigella flexneri 2a

1 reference

12 December 2020

Structure predictions of membrane proteins are not that bad

1 reference

12 December 2020

Carboxy-terminal phenylalanine is essential for the correct assembly of a bacterial outer membrane protein

1 reference

12 December 2020

Identifiers

1 reference

https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:10531204%20AND%20SRC:MED&resulttype=core&format=json

1 November 2019

PubMed publication ID

10531204

1 reference