Finding precursor sequence

Question

[msaranlk]

How to find precursor sequence in est sequence using (subject start and subject end coordinates) blastn result ?

[Prasad]

Could you please elaborate. If you just want the upstream and downstream sequences of start and stop coordinates kindly look @ link1, link2

[msaranlk]

I just need the mathematical explanation also. Example for a est sequence if s.start is 216 and s.end is 236. then if i do upstream and downstream 100. then i get 116 and 336. It mean difference is 336-116=220. so it is not possible to have a precursor length as it. because its range is between 70 to 180. And also, Is it there only one precursor sequence in an est or more.? Then how to do? Do i need to take again upstream and downstream? what is the strategy to do this.? And also there is - strand and + strand. How to handle this for finding this precursor..?

But when I do this to find precursor sequence using mireval online software it give length about all 85. So i think it is not a good way to do with this online software.