The weird insert sequence dominated my library

[skblazer]

Hi,

I constructed an Illumina paired-end library for test, and TOPO cloned an aliquot of the library. I just received six sequence of the picked clones, all of them are adaptered fragments with correct insert size. BUT, only one of the insert fragment are from the genome of my organism. I try to find where are the others from, but I can't find any significant hits using NCBI blastn against nt database. They don't look like dimer, as they are not identical to each other.

Is there anyone have similar experience with this? I know they might be contamination, but I don't know what types of contamination are they, and why they dominate my library?

[pmiguel]

Try a blastx against nr.

What type of PE library did you make? TruSeq? Something else?

If you wanted to post the sequences here, we might find something.

--
Phillip

[skblazer]

Thanks Phillip,

It's just a regular genomic paired-end library, with PE1.0 and PE2.0 as adapters (underlined). I tried blastx, but none of them have significant hits.

I posted three sequence here, thanks for the help:

CAAGCAGAAGACGGCATACGAGATCGGTCTCGGCATTCCTGCTGAACCGCTCTTCCGATCTAATACACTTCTTCCCGCACATCTCGCAGACGTGACTGTCGGCCGGTTTCTTGTAACAGCGCGGCTTGTTCTGTTTCATCTTAAGTCCGAGGTGTACTCTCTGGTAGTGGATCGTGTAGGAACTAGATGACGAAAACGTTAGTTTGCACTGAAAGAATATAAAGTTGATGTATATAATGTGAGAGTAGGCAAACGAGCAGACGGCCTACTTGGTGGTCAGTAGAGATCGGAAGAGCGTCGTGTAGGGAAAGAGTGTAGATCTCGGTGGTCGCCGTATCATT

AATGATACGGCGACCACCGAGATCTACACTCTTTCCCTACACGACGCTCTTCCGATCTTTGACCGTCGATCAGATGCAAAATTTCCTCCTCGTCCAGGTGATGTTCGATATTGTCGGGATTCAGTATGGGTATAGATATGCCCATGTTGTCCAATTTGTCAAGAATCTATTTGGACGCCTTCTTAAATAGTATTTTACCCAAACTAATTATCATGCCTTTCATTTTGATGGAGGACGAGGCGCTGTACAACGCCTTCATTTCCTCCTCAGATCGGAAGAGCGGTTCAGCAGGAATGCCGAGACCGATCTCGTATGCCGTCTTCTGCTTG

CAAGCAGAAGACGGCATACGAGATCGGTCTCGGCATTCCTGCTGAACCGCTCTTCCGATCTGTTGTCCTTCAATTCGCGCAGACGTTTCACGTTCAGGGCGCTTTGGATTTTTTGGGATTGCGTGAGAATACACATGTGTATGCCGAACGGCAGCCTGTCGATGGACATGAAGAACGGATTTCTGGTGTTTATTAACATCCACAACAATCGTTTGACGTGATCGTCACCGCTGCGAATGGCATTTTCGATGGTGGTAGATCGGAAGAGCGTCGTGTAGGGAAAGAGTGTAGATCTCGGTGGTCGCCGTATCATT

Try a blastx against nr.

What type of PE library did you make? TruSeq? Something else?

If you wanted to post the sequences here, we might find something.

--
Phillip

[pmiguel]

Got a couple of hits to the first one in dbest:

[FONT="Courier New"][SIZE="1"]>gb|EY266324.1|  BF01045B2A10.f1 Normalized subtracted keck library BF01 Danaus 
plexippus cDNA clone BF01045B2A10.f1 5, mRNA sequence.
Length=792

 Score =  269 bits (298),  Expect = 3e-69
 Identities = 149/149 (100%), Gaps = 0/149 (0%)
 Strand=Plus/Minus

Query  1    AATACACTTCTTCCCGCACATCTCGCAGACGTGACTGTCGGCCGGTTTCTTGTAACAGCG  60
            ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sbjct  671  AATACACTTCTTCCCGCACATCTCGCAGACGTGACTGTCGGCCGGTTTCTTGTAACAGCG  612

Query  61   CGGCTTGTTCTGTTTCATCTTAAGTCCGAGGTGTACTCTCTGGTAGTGGATCGTGTAGGA  120
            ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sbjct  611  CGGCTTGTTCTGTTTCATCTTAAGTCCGAGGTGTACTCTCTGGTAGTGGATCGTGTAGGA  552

Query  121  ACTAGATGACGAAAACGTTAGTTTGCACT  149
            |||||||||||||||||||||||||||||
Sbjct  551  ACTAGATGACGAAAACGTTAGTTTGCACT  523


>gb|EY270604.1|  BF01052B2H04.f1 Normalized subtracted keck library BF01 Danaus 
plexippus cDNA clone BF01052B2H04.f1 5, mRNA sequence.
Length=668

 Score = 64.4 bits (70),  Expect = 2e-07
 Identities = 55/68 (81%), Gaps = 0/68 (0%)
 Strand=Plus/Plus

Query  155  AATATAAAGTTGATGTATATAATGTGAGAGTAGGCAAACGAGCAGACGGCCTACTTGGTG  214
            |||||| | ||  ||| | | |||| | ||  ||||||||||||||||||||||||||||
Sbjct  144  AATATATATTTATTGTTTTTTATGTTAAAGGTGGCAAACGAGCAGACGGCCTACTTGGTG  203

Query  215  GTCAGTAG  222
            | ||| ||
Sbjct  204  GGCAGCAG  211[/SIZE][/FONT]

If your organism is a butterfly, then I would guess your library may be fine. Just from an organism without its genome in nt.

--
Phillip