Gardara Next we have to specify which type of sequences we want to retrieve, here we are interested in the sequences of the promoter region, starting right next to the coding start of the gene. The exact names that we will have to use to specify the attributes and filters can be retrieved with the listAttributes and listFilters function respectively. This section describes a set of biomaRt helper functions that can be used to export FASTA format sequences, retrieve values for certain filters and exploring the available filters and attributes in a more systematic manner. You still use columns to discover things that can be extracted from a Martand keytypes to discover which things can be used as keys with select.
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This document has the following dependencies: library biomaRt Use the following commands to install these packages in R. R" biocLite c "biomaRt" Improvements and corrections to this document can be submitted on its GitHub in its repository.
Overview We use a large number of different databases in computational biology. The idea is that any kind of resource can setup a Biomart and then users can access the data using a single set of tools to access multiple databases. The biomaRt package implements such an interface. Other Resources The vignette from the biomaRt webpage. Specifiying a mart and a dataset To use biomaRt you need a mart database and a dataset inside the database.
This is somewhat similar to AnnotationHub. You access this database over the internet. Sometimes you need to specify a proxy server for this to work; details are in the biomaRt vignette; I have never encountered this.
This function retrives data from a Biomart based on a query. So it is important to understand how to build queries. Let us do an example. Let us say we want to annotate an Affymetrix gene expression microarray.
We have Affymetrix probe ids in R and we want to retrieve gene names. It is listed under attributes because otherwise it would not appear in the return value of the function. I would just have a list of which genes were measured on the array. An example of a filter that might not appear in the attributes is if you want to only select autosomal genes. You may not care about which chromosomes the different genes appear on, just that they are on autosomal chromosomes. Important note: Biomart at least Ensembl logs how often you query.
If you query to many times, it disable access for a while. So the trick is to make a single vectorized query using a long list of values and not call getBM for each individual value doing this is also much, much slower. A major part of using biomaRt is figuring out which attributes and which filters to use. You can get a description of this using listAttributes and listFilters ; taht returns a very long data. All these entries makes it a bit hard to get a good idea of what is there.
In Biomart, data is organized into pages if you know about databases, this is a non-standard design. Each page contains a subset of attributes. You can get a more understandable set of attributes by using pages.
An attribute can be part of multiple pages. It turns out that getBM can only return a query which uses attributes from a single page. If you want to combine attributes from multiple pages you need to do multiple queries and then merge them. Another aspect of working with getBM is that sometimes the return data. This is a consequence of the internal structure of the database and how queries are interpreted.
The biomaRt vignette is very useful and readable and contains a lot of example tasks, which can inspire future use. As a help, I have listed some of them here: Annotate a set of Affymetrix identifiers with HUGO symbol and chromosomal locations of corresponding genes. Annotate a set of EntrezGene identifiers with GO annotation. Select all Affymetrix identifiers on the hguplus2 chip and Ensembl gene identifiers for genes located on chromosome 16 between basepair and Given a set of EntrezGene identifiers, retrieve bp upstream promoter sequences.
Retrieve known SNPs located on the human chromosome 8 between positions and SessionInfo R version 3.
BIOMART BIOCONDUCTOR PDF
It can annotate a wide range of gene or gene product identifiers e. Furthermore biomaRt enables retrieval of genomic sequences and single nucleotide polymorphism information, which can be used in data analysis. Fast and up-to-date data retrieval is possible as the package executes direct SQL queries to the BioMart databases e. The biomaRt package provides a tight integration of large, public or locally installed BioMart databases with data analysis in Bioconductor creating a powerful environment for biological data mining. Contact: steffen.
BiomaRt, Bioconductor R package