Hi Gaurav,

If your gene with the 3' end His tag is cloned in a plasmid, try to re-order a sequencing primer a little closer to the 3' end. Then re-sequence it. The 'readable'  sequencing result should now cover the 3' end, the His tag codon.

Okay. It means I have to redesign the sequencing primers. 

Thank you

Yes, I am guessing you have cloned your gene with 3'end His tag into a sequencing vector, then used one of their universal primers for sequencing (5' to 3'). Sometimes, the sequencing machine can only give you roughly 500-600 bp readable results. In this case, you can re-design a primer a little closer to the 3' end (it might located in your gene) to give you more readable sequencing results at the 3' end to cover the His tag bases.

Thank you Yuan-Yeu Yau.