non specific amplification in clone fragment using primer

[muhammad yasir]

i use the pcr product of 16s rRNA and i am sure there is no other fragment in this vector, but i am really supresied that amplification of the 1.5kb 16sRNA gene is preety good but getting one week extra band of extactly double size 3Kb. Even i reduced the extension time to 1mints and increase the aneling temp. now the band is more week but still exsist.
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