RNA-seq Bioinformatics

Introduction to bioinformatics for RNA sequence analysis


Getting Started

This tutorial assumes use of a Linux computer with an ‘x86_64’ architecture. The rest of the tutorial should be conducted in a linux Terminal session. In other words you must already be logged into the Amazon EC2 instance as described in the previous section.

Before proceeding you must define a global working directory by setting the environment variable: ‘RNA_HOME’ Log into a server and SET THIS BEFORE RUNNING EVERYTHING.

Create a working directory and set the ‘RNA_HOME’ environment variable

mkdir -p ~/workspace/rnaseq/

export RNA_HOME=~/workspace/rnaseq

Make sure whatever the working dir is, that it is set and is valid

echo $RNA_HOME

You can place the RNA_HOME variable (and other environment variables) in your .bashrc and then logout and login again to avoid having to worry about it. A .bashrc file with these variables has already been created for you. It also includes module load commands for software needed on Compute Canada which are described here.

In order to use this file, you must first copy the .bashrc file to your home directory and then source it.

cp ~/CourseData/.bashrc ~
source ~/.bashrc

Environment variables used throughout this tutorial:

export RNA_HOME=~/workspace/rnaseq
export RNA_DATA_DIR=$RNA_HOME/data
export RNA_REFS_DIR=$RNA_HOME/refs
export RNA_REF_INDEX=$RNA_REFS_DIR/chr22_with_ERCC92
export RNA_ALIGN_DIR=$RNA_HOME/alignments/hisat2

We will be using picard tools throughout this workshop. To follow along, you will need to set an environment variable pointing to your picard installation. For the Compute Canada cluster:

export PICARD=$EBROOTPICARD/picard.jar

When using a student AWS instance:

export PICARD=$RNA_HOME/student_tools/picard.jar

If these variables are not part of your .bashrc, you can type the following. First, you can open your .bashrc file with nano by simply typing:

nano ~/.bashrc

You can now see the contents of this file. Then, you want to add the above environment variables to the bottom of the file. You can do this by copying and pasting. Once you have the variables in the file, you’ll want to type ctrl + o to save the file, then enter to confirm you want the same filename, then ctrl + x to exit nano.

Since all the environment variables we set up for the RNA-seq workshop start with ‘RNA’ we can easily view them all by combined use of the env and grep commands as shown below. The env command shows all environment variables currently defined and the grep command identifies string matches.

env | grep RNA