GO Annotation File (GAF) Format 2.0

Annotation data is submitted to the GO Consortium in the form of gene association files, or GAFs. This guide lays out the format specifications for GAF 2.0; for the older GAF 1.0 file syntax, please see the GAF 1.0 file format guide.

Please see the information on the changes in GAF 2.0.

More general information on annotation can be found in the GO annotation guide.

Changes in GAF 2.0

GAF 2.0 has two additional columns compared to GAF 1.0: annotation extension (column 16) and gene product form ID (column 17).

The addition of gene product form ID (column 17) means that the usage of the DB object ID (column 2) and DB object type (column 12) fields differs from that in GAF 1.0. Please see the descriptions below for full details.

File Header

All gene association files must start with a single line denoting the file format, as follows:

!gaf-version: 2.0

Other information, such as contact details for the submitter or database group, useful link, etc., can be included in an association file by prefixing the line with an exclamation mark (!); such lines will be ignored by parsers.

Annotation File Fields

The annotation flat file format is comprised of 17 tab-delimited fields.

Column Content Required? Cardinality Example
1 DB required 1 UniProtKB
2 DB Object ID required 1 P12345
3 DB Object Symbol required 1 PHO3
4 Qualifier optional 0 or greater NOT
5 GO ID required 1 GO:0003993
6 DB:Reference (|DB:Reference) required 1 or greater PMID:2676709
7 Evidence Code required 1 IMP
8 With (or) From optional 0 or greater GO:0000346
9 Aspect required 1 F
10 DB Object Name optional 0 or 1 Toll-like receptor 4
11 DB Object Synonym (|Synonym) optional 0 or greater hToll|Tollbooth
12 DB Object Type required 1 protein
13 Taxon(|taxon) required 1 or 2 taxon:9606
14 Date required 1 20090118
15 Assigned By required 1 SGD
16 Annotation Extension optional 0 or greater part_of(CL:0000576)
17 Gene Product Form ID optional 0 or 1 UniProtKB:P12345-2

 

Definitions and requirements for field contents

DB (column 1)
refers to the database from which the identifier in DB object ID (column 2) is drawn. This is not necessarily the group submitting the file. If a UniProtKB ID is the DB object ID (column 2), DB (column 1) should be UniProtKB.
must be one of the values from the set of GO database cross-references
this field is mandatory, cardinality 1

 

DB Object ID (column 2)
a unique identifier from the database in DB (column 1) for the item being annotated
this field is mandatory, cardinality 1
In GAF 2.0 format, the identifier must reference a top-level primary gene or gene product identifier: either a gene, or a protein that has a 1:1 correspondence to a gene. Identifiers referring to particular protein isoforms or post-translationally cleaved or modified proteins are not legal values in this field.
The DB object ID (column 2) is the identifier for the database object, which may or may not correspond exactly to what is described in a paper. For example, a paper describing a protein may support annotations to the gene encoding the protein (gene ID in DB object ID field) or annotations to a protein object (protein ID in DB object ID field).

 

DB Object Symbol (column 3)
a (unique and valid) symbol to which DB object ID is matched
can use ORF name for otherwise unnamed gene or protein
if gene products are annotated, can use gene product symbol if available, or many gene product annotation entries can share a gene symbol this field is mandatory, cardinality 1
The DB Object Symbol field should be a symbol that means something to a biologist wherever possible (a gene symbol, for example). It is not an ID or an accession number (DB object ID [column 2] provides the unique identifier), although IDs can be used as a DB object symbol if there is no more biologically meaningful symbol available (e.g., when an unnamed gene is annotated).

 

Qualifier (column 4)
flags that modify the interpretation of an annotation
one (or more) of NOT, contributes_to, colocalizes_with
this field is not mandatory; cardinality 0, 1, >1; for cardinality >1 use a pipe to separate entries (e.g. NOT|contributes_to)
See also the documentation on qualifiers in the GO annotation guide

 

GO ID (column 5)
the GO identifier for the term attributed to the DB object ID
this field is mandatory, cardinality 1

 

DB:Reference (column 6)
one or more unique identifiers for a single source cited as an authority for the attribution of the GO ID to the DB object ID. This may be a literature reference or a database record. The syntax is DB:accession_number.
Note that only one reference can be cited on a single line in the gene association file. If a reference has identifiers in more than one database, multiple identifiers for that reference can be included on a single line. For example, if the reference is a published paper that has a PubMed ID, we strongly recommend that the PubMed ID be included, as well as an identifier within a model organism database. Note that if the model organism database has an identifier for the reference, that identifier should always be included, even if a PubMed ID is also used.
this field is mandatory, cardinality 1, >1; for cardinality >1 use a pipe to separate entries (e.g. SGD_REF:S000047763|PMID:2676709).

 

Evidence Code (column 7)
see the GO evidence code guide for the list of valid evidence codes for GO annotations
this field is mandatory, cardinality 1

 

With [or] From (column 8)
Also referred to as with, from or the with/from column
one of:
  • DB:gene_symbol
  • DB:gene_symbol[allele_symbol]
  • DB:gene_id
  • DB:protein_name
  • DB:sequence_id
  • GO:GO_id
  • CHEBI:CHEBI_id
this field is not mandatory overall, but is required for some evidence codes (see below and the evidence code documentation for details); cardinality 0, 1, >1; for cardinality >1 use a pipe to separate entries (e.g. CGSC:pabA|CGSC:pabB)
Note: This field is used to hold an additional identifier for annotations using certain evidence codes (IC, IEA, IGI, IPI, ISS). For example, it can identify another gene product to which the annotated gene product is similar (ISS) or interacts with (IPI). More information on the meaning of with or from column entries is available in the evidence code documentation entries for the relevant codes.
Cardinality = 0 is not recommended, but is permitted because cases can be found in literature where no database identifier can be found (e.g. physical interaction or sequence similarity to a protein, but no ID provided). Cardinality = 0 is not allowed for ISS annotations made after October 1, 2006. Annotations where evidence is IGI, IPI, or ISS and with cardinality = 0 should link to an explanation of why there is no entry in with. Cardinality may be >1 for any of the evidence codes that use with; for IPI and IGI cardinality >1 has a special meaning (see evidence documentation for more information). For cardinality >1 use a pipe to separate entries (e.g. FB:FBgn1111111|FB:FBgn2222222).
Note that a gene ID may be used in the with column for a IPI annotation, or for an ISS annotation based on amino acid sequence or protein structure similarity, if the database does not have identifiers for individual gene products. A gene ID may also be used if the cited reference provides enough information to determine which gene ID should be used, but not enough to establish which protein ID is correct.
'GO:GO_id' is used only when the evidence code is IC, and refers to the GO term(s) used as the basis of a curator inference. In these cases the entry in the 'DB:Reference' column will be that used to assign the GO term(s) from which the inference is made. This field is mandatory for evidence code IC.
The ID is usually an identifier for an individual entry in a database (such as a sequence ID, gene ID, GO ID, etc.). Identifiers from the Center for Biological Sequence Analysis (CBS), however, represent tools used to find homology or sequence similarity; these identifiers can be used in the with column for ISS annotations.
The with column may not be used with the evidence codes IDA, TAS, NAS, or ND.

 

Aspect (column 9)
refers to the namespace or ontology to which the GO ID (column 5) belongs; one of P (biological process), F (molecular function) or C (cellular component)
this field is mandatory; cardinality 1

 

DB Object Name (column 10)
name of gene or gene product
this field is not mandatory, cardinality 0, 1 [white space allowed]

 

DB Object Synonym (column 11)
Gene symbol [or other text] Note that we strongly recommend that gene synonyms are included in the gene association file, as this aids the searching of GO.
this field is not mandatory, cardinality 0, 1, >1 [white space allowed]; for cardinality >1 use a pipe to separate entries (e.g. YFL039C|ABY1|END7|actin gene)

 

DB Object Type (column 12)
A description of the type of gene product being annotated. If a gene product form ID (column 17) is supplied, the DB object type will refer to that entity; if no gene product form ID is present, it will refer to the entity that the DB object symbol (column 2) is believed to produce and which actively carries out the function or localization described. one of the following: protein_complex; protein; transcript; ncRNA; rRNA; tRNA; snRNA; snoRNA; any subtype of ncRNA in the Sequence Ontology. If the precise product type is unknown, gene_product should be used. this field is mandatory, cardinality 1
The object type (gene_product, transcript, protein, protein_complex, etc.) listed in the DB object type field must match the database entry identified by the gene product form ID, or, if this is absent, the expected product of the DB object ID. Note that DB object type refers to the database entry (i.e. it represents a protein, functional RNA, etc.); this column does not reflect anything about the GO term or the evidence on which the annotation is based. For example, if your database entry represents a protein-encoding gene, then protein goes in the DB object type column. The text entered in the DB object name and DB object symbol should refer to the entity in DB object ID. For example, several alternative transcripts from one gene may be annotated separately, each with the same gene ID in DB object ID, and specific gene product identifiers in gene product form ID, but list the same gene symbol in the DB object symbol column.

 

Taxon (column 13)
taxonomic identifier(s) For cardinality 1, the ID of the species encoding the gene product. For cardinality 2, to be used only in conjunction with terms that have the biological process term multi-organism process or the cellular component term host cell as an ancestor. The first taxon ID should be that of the organism encoding the gene or gene product, and the taxon ID after the pipe should be that of the other organism in the interaction. this field is mandatory, cardinality 1, 2; for cardinality 2 use a pipe to separate entries (e.g. taxon:1|taxon:1000) See the GO annotation conventions for more information on multi-organism terms.

 

Date (column 14)
Date on which the annotation was made; format is YYYYMMDD
this field is mandatory, cardinality 1

 

Assigned By (column 15)
The database which made the annotation
one of the values from the set of GO database cross-references
Used for tracking the source of an individual annotation. Default value is value entered as the DB (column 1).
Value will differ from column 1 for any annotation that is made by one database and incorporated into another.
this field is mandatory, cardinality 1

 

Annotation Extension (column 16)
one of:
  • DB:gene_id
  • DB:sequence_id
  • CHEBI:CHEBI_id
  • Cell Type Ontology:CL_id
  • GO:GO_id
Contains cross references to other ontologies that can be used to qualify or enhance the annotation. The cross-reference is prefaced by an appropriate GO relationship; references to multiple ontologies can be entered. For example, if a gene product is localized to the mitochondria of lymphocytes, the GO ID (column 5) would be mitochondrion ; GO:0005439, and the annotation extension column would contain a cross-reference to the term lymphocyte from the Cell Type Ontology.
Targets of certain processes or functions can also be included in this field to indicate the gene, gene product, or chemical involved; for example, if a gene product is annotated to protein kinase activity, the annotation extension column would contain the UniProtKB protein ID for the protein phosphorylated in the reaction.
See the documentation on using the annotation extension column for details of practical usage; a wider discussion of the annotation extension column can be found on the GO wiki.
this field is optional, cardinality 0 or greater

 

Gene Product Form ID (column 17)
As the DB Object ID (column 2) entry must be a canonical entity—a gene OR an abstract protein that has a 1:1 correspondence to a gene—this field allows the annotation of specific variants of that gene or gene product. Contents will frequently include protein sequence identifiers: for example, identifiers that specify distinct proteins produced by to differential splicing, alternative translational starts, post-translational cleavage or post-translational modification. Identifiers for functional RNAs can also be included in this column.
The identifier used must be a standard 2-part global identifier, e.g. UniProtKB:OK0206-2
  • When the gene product form ID (column 17) is filled with a protein identifier, the value in DB object type (column 12) must be protein. Protein identifiers can include UniProtKB accession numbers, NCBI NP identifiers or Protein Ontology (PRO) identifiers.
  • When the gene product form ID (column 17) is filled with a functional RNA identifier, the DB object type (column 12) must be either ncRNA, rRNA, tRNA, snRNA, or snoRNA.
This column may be left blank; if so, the value in DB object type (column 12) will provide a description of the expected gene product.
More information and examples are available from the GO wiki page on column 17.

Note that several fields contain database cross-reference (dbxrefs) in the format dbname:dbaccession. The fields are: GO ID [column 5], where dbname is always GO; DB:Reference (column 6); With or From (column 8); and Taxon (column 13), where dbname is always taxon. For GO IDs, do not repeat the 'GO:' prefix (i.e. always use GO:0000000, not GO:GO:0000000)