INTRODUCTION TO BLAST

BLAST is database search tool,developed and maintained primarily by national center for biotechnological information(ncbi).the web based tool is avaliable at http://www.ncbi.nlm.nih.gov/BLAST/ .The BLAST suite of programs has been designed to find out high scoring local alignment between sequences,without compromising the speed of such searches.BLAST uses a heuristic algorithm which seeks local alignments and is able to detect relationship among sequences which share only isolated regions of similarity.The first version of blast was released in 1990 and allow users to perform ungapped searches only.The second version of blast released in 1997,allowed gap seaches.


BLAST ANALYSIS:-

to use blast,we need to select
1.an input query sequence(either nucleotides or protein)
2.The database released to seach against(either nuleotide or protein)
3.A database search program(any of the five avaliable with blast)


STEPS INVOLVED IN USING BLAST TOOL:-
(protein sequence)
Step1:-
Go to the blast page at NCBI and click on the link blastp.

Step2:-
Paste the query sequence in fasta format in the data entry field.

Step3:-The important field is a drop down menu that allows the selection of the database to use for compare.

Step4:-Now,filtering option is done which ensures that no false positive hits/result are obtained due to short sequence.

Step5:-Now click on blast button to run the blastp seach.

Step6:-
A new page will appear showing the ID number of the search and percentage of identity between the sequences.


INTERPRETATIONG BLAST RESULT:-
Step1:-
The blast result page begins with the program version used,the refrence for blast ,the name and length of the query sequence ,the database searched and contact information.

Step2:-
Next it shows the number of hits obtained on the query sequence and a graphical overview of the alignment of the hits to the query.

Step3:-
A long rod line near the top of the graphical overview represents the length of the query sequence.each colured line below the query sequence repesents a hit obtained from the database.

Step4:-
The graphical overview shows the relative position of similar regions in each hit and query.the details also provide the percentage of similarity/identity between the query and hit.