Sam:LabNotes/Microbiome-new/2010-4-16

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Revision as of 07:57, 17 April 2010 by >Sam Chiang (→‎Results)
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Sanger sequencing troble shooting - mp1-mp8 amplicons (PCR products from 04-04-'10)

Background

  • The the 2nd Sanger seqeuencing was performed with special "very-short PCR primer"(The primer modifie from regular library amplification primer with no extension tail and only 21nt => Tm=59).
  • The Sanger sequencing results still showed a very low sequence quality due to the unspecific amplicons.

Possible reasons and improvements (Discussed with technical support):

  • There are unspecific amplification. Unspecific amplication were difficul to be seen and removed by E-gel and still could be amplified in the 2nd round PCR.
    • Sol.1 => Use the old school trick to do gel cutting on target band for sequencing.
    • Sol.2 => Increase the annealing temperature. Choose the good annealing temp by doing a gradient PCR.
  • The original templates (insert) have contaminations.
    • The original inserts of these libraries is PCR product, probably the inserts originally contain the contamination.
    • Since I am using the primers that can bind on adaptors, any thing ligated by the adaptor could be amplified.
    • I assume that Sanger sequencing using Lib. amplification primer is more difficult then using gene specific primers, in terms of getting good quality of sequencing results.

Optimizing annealing tempurature

  • Test possible annealing temputrature beteen 50C~70C using gradient PCR program (Program: G-PCR) - program set up (07-01-2009)
               1rxn     8.5rxn x 2
H2O            10.0     85.0
DNA             0.5      4.25
Primer-f(10uM)  1.0      8.50 ----- "short-PCR primer" / "very-short PCR primer"
Primer-r(10uM)  1.0      8.50 ----- "short-PCR primer" / "very-short PCR primer"  
2X Fusion      12.5    105.25
-----------------------------
               25.0    212.5 / 8.5=25
NOTE:
1. The expected Annealing temp for short-PCR primeris 64.
2. The expected Annealing temp for very-short-PCR primer is 59.

Results

  • PCR program (G-PCR):
Step1  94C 2min
Step2  94C 40sec
Step3  50C-70C 40sec
Step4  72C 1min
Step5  Goto step2 for 34 cycles
Step6  72C 10min
Step7  End
File:Sam041610-gradient PCR on short -PCR primer.jpg File:Sam041610-gradient PCR on very-short -PCR primer.jpg