I have few questions regarding the nr database.
As per the instruction manual README2.1.txt, the sequence database nr.tar.gz can either be downloaded from the umich website or it can be obtained from the NCBI with the later one always recommended.
However, there are noticeable differences. The version on the NCBI website is almost 3~4 GB bigger than the one from umich website.
Secondly, the one from the NCBI comes in two different formats. One format has it broken into 16 files and is available at BLAST-DB whereas the other one is provided as a whole at BLAST-DB-FASTA.
Can somebody please explain why NCBI version is bigger? Is the umich version not complete? Where is the difference coming from?
If I were to set up my system to update it every week from the NCBI website, what steps should I take? Do I need to download the blast program?
Should I download the files every week from NCBI website? How do I combine the 16 files from the NCBI website?
Do I need the blast program from the NCBI website to update the nr database?