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    Affordable method for genotyping HIV-1 reverse transcriptase, protease and integrase genes: an in-house protocol

    Sontaga Manyana, Melendhran Pillay, Lilishia Gounder, Aabida Khan, Pravi Moodley, Kogieleum Naidoo, Benjamin Chimukangara

    Published: 2023-02-13 DOI: 10.17504/protocols.io.b5tvq6n6
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    Abstract

    HIV drug resistance (HIVDR) remains a major threat to achieving sustainable viral suppression on antiretroviral treatment. To overcome concerns over increasing levels in pretreatment drug resistance and subsequent cost implications, most countries including those in resource limited settings (RLS) adopted use of dolutegravir (DTG), a potent integrase strand transfer inhibitor (INSTI). As more people receive INSTIs, the demand for INSTI resistance testing is increasing. Current HIVDR testing methods in RLS focus on genotyping HIV protease (PR) and reverse transcriptase (RT) genes, separate from the integrase (IN) gene. However, such an approach is expensive and evidently increases the workload for HIVDR genotyping. As a result, affordable and labour efficient methods that genotype all relevant HIV-1 genes (i.e., the PR, RT and IN genes) are required to guide clinical decisions, especially in RLS where cost is a major limiting factor. Therefore, we developed a protocol for genotyping complete HIV-1C genes at an affordable cost and time-efficient manner, that can be adopted for use in HIV drug resistance genotyping. The main limitation to this protocol is that it was only tested on HIV-1C samples, and thus might not be effective against other HIV subtypes. In conclusion, the expected results of using this protocol include complete HIV-1C sequence coverage of all relevant viral gene regions; i.e. PR codons 1 - 99, RT codons 1 - 560, and IN codons 1 - 288, for HIVDR genotyping.

    Before start

    Ensure that the working areas are disinfected

    • Remember to check the expiring date of the reagents before use

    • Ensure that instruments maintenance is up to date

    Steps

    EXTRACTION

    1.

    Sample preparation and RNA extraction on NucliSENS easyMAG

    1.1.

    Retrieve plasma samples from -80°C freezer and leave to equilibrate to room temperature prior to processing.

    1.10.

    Vortex magnetic silica briefly and add 50µL to numbered NucliSENS easyMAG consumables.

    1.11.

    Using a BioHit multichannel pipette set at P3, mix sample solution with magnetic silica by pipetting up and down, avoiding bubbles. Remove excess bubbles if necessary.

    1.12.

    Load NucliSENS easyMAG consumables on to the NucliSENS easyMAG instrument and scan barcodes on consumables.

    1.13.

    Program NucliSENS easyMAG instrument and select 25µL elution volume.

    1.14.

    Start extraction run.

    Note
    The run will take ~0h 35m 0s

    1.15.

    After extraction is complete, transfer eluent into appropriately labelled1.5mL microcentrifuge tubes.

    1.16.

    Discard NucliSENSeasyMAG consumables appropriately as biohazard waste.

    1.17.

    Proceed to perform PCR amplification or store RNA at -80°C until use.

    1.2.

    Transfer 500µLof plasma into well labeled 1.5mL Sarstedt screw-cap tubes/ eppendorf tubes and place in a pre-cooled microcentrifuge at 4°C.

    1.3.

    Mark the top of each tube on the outside and spin at 23000x g,0h 0m 0s for 1h 0m 0sat 4°C.

    1.4.

    After spinning, remove 300µL of supernatant and briefly vortex the ~200µL pellet.

    Note
    Preferably remove ~280µLto ensure you have at least 200µL of pellet remaining. Pipette from the opposite side of the mark on the top of the tube.

    1.5.

    Proceed to extraction room

    Note
    Prior to extraction, make 400µL aliquots of lysis buffer and remove magnetic silica from fridge and equilibrate to room temperature.

    1.6.

    Pipette mix the 200µL pellet and transfer to400µL of lysis buffer.

    1.7.

    Vortex briefly and incubate at room temperature for 0h 20m 0s.

    1.8.

    While the sample is lysing, label disposable NucliSENS easyMAG consumables according to sample list.

    1.9.

    After incubation, transfer lysate (~600µL) into respective wells of NucliSENS easyMAG consumables.

    PCR MASTER MIX

    2.

    Preparation of one-step reverse transcription and second-round PCR master mix

    2.1.

    Proceed to PCR master mix room (i.e. clean room).

    2.2.

    All reagents except the enzymes (Superscript IV and Platinum Taq DNA Polymerase) must be thawed and vortexed for 0h 0m 5s to 0h 0m 10s

    2.3.

    Label reverse transcription and second-round PCR tubes 0.2mL with sample numbers, accordingly.

    2.4.

    Label two 1.5mL microcentrifuge tubes as follows; Tube 1: for RT one-step PCR master mix, and Tube 2: for second-round PCR master mix.

    Note
    Prepare each master mix for the number of specimens to be amplified, including a negative control, and positive control.

    Note
    Add reagents in order listed in Table 1, and make two extra volumes to account for pipetting errors.

    2.5.

    Prepare RT-PCR master mix as shown in Table 1, using Superscript IV one-step PCR reagents.

    ABC
    ReagentsVolume per reaction (µl)Concentration per reaction
    2X Reaction RT-PCR master mix12.51X
    Nuclease-free Water2.25-
    PANA2AF (5µM)2.50.5µM
    PANA3AR (5µM)2.50.5µM
    SSIV/ Platinum SuperFi DNA polymerase (2X)0.250.02X
    Total volume20-

    Table 1. One-step reverse transcription PCR master mix.

    Note
    Details of primers for one-step RT-PCR master mix are shown in Table 2.

    ABC
    Primer name (Direction)Primer sequenceHXB2
    PANA2AF (Forward)GAGGCAATGAGCCAARCAAACA1882 - 1903
    PANA3AR (Reverse)TTCCAGGGCTCTAGKTTAGG5846 - 5865

    Table 2. Details of primers used in one-step reverse transcription PCR master mix.

    Note
    Add reagents in order listed in Table 3, and make two extra volumes to account for pipetting errors.

    2.6.

    Prepare master mix for the second-round PCR as shown in Table 3, using Platinum Taq PCR reagents.

    ABC
    Second-round PCR Mastermix
    ReagentVolume per reaction (µl)Concentration per reaction
    Nuclease-free Water18.4-
    10X PCR Buffer2.51X
    MgCl2 (50mM)1.02mM
    dNTP (10mM)0.50.2mM
    Pro1 (5µM)0.250.05µM
    5066R (5µM)0.250.05µM
    Platinum Taq DNA Polymerase0.1-
    Total volume23-

    Table 3. Second-round PCR master mix.

    Details of primers for second-round PCR master mix are shown in Table 4.

    ABC
    Primer name (Direction)Primer sequencesHXB2
    Pro1 (Forward)TAGAGCCAACAGCCCCACCA2147 - 2166
    5066R (Reverse)ATCATCACCTGCCATCTGTTTTCCAT5041 - 5066

    Table 4. Details of primers used in second-round PCR.

    2.7.

    Mix one-step RT-PCR master mix by pipetting up and down (or by gently tapping the tube), and transfer 20µLto the respective 0.2µL PCR tubes.

    2.8.

    Mix second-round PCR master mix by pipetting up and down (or by gently tapping the tube), and transfer 23µLto the respective 0.2µL PCR tubes.

    2.9.

    Take aliquoted one-step RT-PCR master mix into the extraction laboratory (or dead air space cabinet in general laboratory).

    Note
    Store second-round PCR master mix at -20°C until use.

    ADDING RNA

    3.

    Adding RNA to one-step RT-PCR master mix.

    3.1.

    Proceed to extraction laboratory, or dead air space cabinet.

    3.2.

    Thaw RNA, gently tap tubes, and briefly spin.

    3.3.

    Add 5µL RNA to respective tubes containing master mix.

    Note
    Add 5µL of nuclease free water to negative control. Total reaction volume is 25µL.

    3.4.

    Proceed to the PCR amplification room.

    ONE-STEP RT-PCR

    4.

    RT-PCR amplification process.

    4.1.

    Gently tap PCR tubes to mix and centrifuge briefly.

    4.2.

    Switch on thermal cycler and wait for the instrument to initialize.

    4.3.

    Place tubes in thermal cycler and run the conditions shown in Table 5.

    ABCD
    Thermocycling conditionsTemperature (degrees celcius)TimeCycle(s)
    cDNA synthesis5010 minutes1
    Pre-denaturation982 minutes1
    Denaturation9810 seconds40
    Annealing5620 seconds
    Extension722 minutes
    Final extension7210 minutes
    Hold4∞Hold

    Table 5. One-step RT-PCR amplification conditions.

    Note
    PCR run takes ~2h 35m 0s

    4.4.

    After PCR is complete, remove PCR tubes from thermal cycler and proceed to second-round PCR amplification, or store at -20°C.

    SECOND-ROUND PCR

    5.

    Second-round PCR amplification.

    5.1.

    In PCR amplification laboratory, remove second-round PCR master mix from-20°C.

    5.2.

    Gently mix one-step RT-PCR amplicons by pipetting up and down, and add 2µL to the respective second-round PCR master mix tubes.

    Note
    Total reaction volume is 25µL.

    5.3.

    Gently tap PCR tubes and centrifuge briefly.

    5.4.

    Place the PCR tubes in thermal cycler and run the conditions shown in Table 6.

    ABCD
    Thermocycling conditionsTemperature (degrees celcius)TimeCycle(s)
    Pre-denaturation942 minutes1
    Denaturation9510 seconds40
    Annealing5620 seconds
    Extension722 minutes
    Final extension7210 minutes1
    Hold4∞Hold

    Table 6. Second-round PCR amplification conditions.

    Note
    PCR run takes ~2h 15m 0s.

    5.5.

    After PCR is complete, remove PCR tubes from thermal cycler and proceed to run gel electrophoresis, or store second-round amplicons at -20°C.

    DETECTION OF AMPLICONS

    6.

    Gel electrophoresis on agarose gel.

    6.1.

    Assemble gel casting apparatus by securing gel casting gates on both sides of the casting tray. Place gel comb in upper slot of the casting tray.

    6.10.

    Add 1µL of gel loading dye to a piece of parafilm paper for each amplicon to be loaded on the gel.

    6.11.

    Mix with 5µL of each amplicon and load into respective wells of the agarose gel.

    Note
    Preferably, start loading amplicons from the second well, taking note of the order by which the amplicons are loaded.

    6.12.

    Mix 3µL of gel loading dye with 3µL of DNA ladder, and load into the first well of the agarose gel.

    6.13.

    Close the lid of the electrophoresis tank ensuring that the negative electrode (black) is positioned close to the agarose gel wells.

    6.14.

    Switch PowerPac on and set voltage at 120V.

    6.15.

    Run the gel for at least 0h 45m 0s.

    Note
    Check for bubbles at negative electrode (black) to ensure there is current running through the tank.

    6.16.

    After running gel, remove it from electrophoresis tank and visualize on BioMetra UV detection unit.

    6.17.

    PCR amplicons should be at a size of approximately 2.9 kilobases (kb) as measured against the DNA ladder in well position 1.

    Note
    For a valid PCR run, the positive control should have a band at approximately 2.9kb, and the negative control should not have a band.

    6.18.

    Proceed to PCR product purification or store amplicons at -20°C until use.

    6.2.

    Prepare 1X TBE by adding 1 part 10X TBE buffer to 9 parts distilled water. For example to make 1L of 1X TBE, mix 100mLof 10X TBE with 900mL of distilled water.

    6.3.

    Prepare 1% agarose gel by adding two 0.5g agarose tablets to 100mL of 1X TBE in a Schott bottle.

    Note
    Break agarose tablets in half before adding to 1X TBE, and wait briefly for tablets to dissolve before heating in microwave.

    6.4.

    Heat in microwave for approximately 0h 2m 0s, swirling occasionally to ensure agarose tablets have dissolved completely.

    Note
    Take care that the gel-mix does not boil over.

    6.5.

    Gently remove from microwave taking care not to spill over and allow cooling at room temperature, or by running the base of the flask under cold water.

    Note
    The gel is cool enough when you are able to comfortably touch the gel bottle for 0h 0m 3s to 0h 0m 5s.

    6.6.

    Add 10µL of SYBR safe gel stain (10,000X concentrate) to 100mL gel.

    Note
    Add 1µL of SYBR safe gel stain (10,000X concentrate) for every 10mL) of agarose gel mix.

    6.7.

    Allow agarose gel to set (~0h 30m 0s).

    6.8.

    Once set, carefully remove gel comb and the casting gates.

    6.9.

    Place agarose gel in the electrophoresis tank with wells closest to the anode (i.e. negative electrode (black) position on top) and immerse in 1X TBE buffer.

    PCR PRODUCT PURIFICATION

    7.

    PCR product purification using ExoSAP-IT PCR production purification

    7.1.

    For samples with successful amplification, label PCR tubes required for purification.

    7.2.

    Tap amplicon tubes gently to mix and briefly spin to bring the contents to bottom of tube .

    Note
    If frozen, first thaw the amplicons to room temperature.

    7.3.

    Remove ExoSAP-IT Express reagent from -20°C freezer.

    7.4.

    Gently tap ExoSAP-IT Express reagent to mix and briefly spin to bring contents to bottom of tube.

    7.5.

    Mix 10µL of PCR amplicon with4µL of ExoSAP-IT Express reagent for a combined 14µL reaction volume.

    7.6.

    Mix thoroughly by tapping the tube and quick spin to bring contents to the bottom of the tube .

    7.7.

    Place the tubes in thermal cycler and run the conditions shown in Table 7.

    ABCD
    Thermocycling conditionsTemperature (degrees celcius)TimeCycle(s)
    Cleanup374 minutes1
    Enzyme inactivation801 minute1
    Hold4∞Hold

    Table 7. PCR purification conditions.

    7.8.

    After ~0h 5m 0s on thermal cycler, purified PCR products are ready for DNA sequencing.

    Note
    Purified PCR products may be stored at -20°Cuntil use.

    CYCLE SEQUENCING REACTION AND PURIFICATION

    8.

    BigDye cycle sequencing.

    8.1.

    The following procedure is used to set up the sequencing reaction mix using BigDye Terminator v3.1 cycle sequencing kit (LifeTechnologies) with 8 primers per sample.

    8.10.

    Cover plate with aluminium plate seal, tap plate gently to mix, and spin plate briefly.

    8.11.

    Remove aluminium plate seal and cover plate with PCR septa mat.

    8.12.

    Place on thermal cycler and run the conditions shown in Table 10.

    ABCD
    Thermocycling conditionsTemperature (degrees celcius)TimeCycle(s)
    Pre-denaturation961 minutes1
    Denaturation9610 seconds35
    Annealing505 seconds
    Extension604 minutes
    Hold4∞

    Table 10. Cycle sequencing reaction conditions.

    8.13.

    After the cycle sequencing reaction run is complete, proceed with BigDye sequencing reaction purification, or store the plate covered in foil at 4°Cfor up to 1 week, or at -20°Cfor storage longer than 1 week .

    8.14.

    Remove SAM and XTerminator reagents from fridge (stored at 4°C) and equilibrate to room temperature prior to preparing SAM/BigDye XTerminator mix.

    Note
    The BigDye XTerminator Purification kit (Life Technologies) is used to purify sequencing reaction products. The kit consists of 2 reagents; XTerminator solution and SAM solution.

    8.15.

    Following BigDye cycle sequencing reaction, centrifuge 96-well reaction plate at 4000rpm,0h 0m 0s for 0h 1m 0s.

    8.16.

    Thoroughly vortex XTerminator solution for at least0h 0m 30s.

    8.17.

    Prepare the SAM/BigDye XTerminator bead working solution in a 50mL Falcon tube, by adding reagent volumes shown in Table 11.

    AB
    ComponentVolume per 10μL reaction
    SAM solution45μL
    BigDye XTerminator solution10μL
    Total volume55μL

    Note
    Preferably use wide-orifice tips when pipetting BigDye XTerminator solution.

    8.18.

    Mix the SAM/BigDye XTerminator bead working solution thoroughly by vortexing and dispense in a reagent reservoir.

    8.19.

    Remove PCR septa mat from 96-well reaction plate and add 55µLof SAM/BigDye XTerminator bead working solution to each well.

    Note
    Preferably use a multi-channel pipette to add reagent mix, changing tips each time.

    8.2.

    Thaw all reagents at room temperature.

    8.20.

    Cover plate with aluminium plate seal.

    8.21.

    Vortex plate on a plate shaker at 1800rpm,0h 0m 0s for 0h 30m 0s.

    8.22.

    After vortexing, centrifuge plate at 4000rpm,0h 0m 0s for 0h 2m 0s.

    Note
    If the reaction plates are not run immediately, you can store them under the following conditions: Room temperature (i.e. 20°C - 25°C): Store plates sealed with adhesive film or septa for up to 2 days.Refrigerated storage (4°C): Store plates sealed with adhesive film for up to 10 days. Frozen storage (-20°C): Store plates sealed with adhesive film for up to 10 days.

    8.3.

    Label eight 1.5mL tubes, one for each primer mix.

    8.4.

    Vortex sequencing buffer and primers and briefly spin to bring contents to the bottom of the tube.

    8.5.

    Mix BigDye reagent by tapping tube and briefly spin to bring contents to bottom of tube.

    Note
    Add reagents in order listed in Table 8, and make two extra volumes to account for pipetting errors.

    8.6.

    Prepare master mix for each primer as shown in Table 8.

    ABC
    ReagentVolume (µl)/ reactionConcentration per reaction
    Nuclease-free Water6.1-
    5X Sequencing buffer21X
    Primer (3.2µM)0.50.2µM
    BigDye Sequencing mix0.4-
    Total9.0

    Table 8. BigDye cycle sequencing reaction mix.

    Note
    Details of sequencing primers are shown in Table 9.

    ABCD
    Primer (Direction)Primer sequenceHXB2Gene
    RTC1F (Forward)ACCTACACCTGTCAACATAATTG2486 - 2508PR and RT
    RTC2R (Reverse)TGTCAATGGCCATTGTTTAACCTTTGG2630 - 2604PR and RT
    RTC3F (Forward)CACCAGGGATTAGATATCAATATAATGTGC2965 - 2994PR and RT
    RTC4R (Reverse)CTAAATCAGATCCTACATACAAGTCATCC3101 - 3129PR and RT
    KVL076 (Forward)GCACAYAAAGGRATTGGAGGAAATGAAC4161 - 4188IN
    KVL082 (Forward)GGVATTCCCTACAATCCCCAAAG4647 - 4669IN
    KVL083 (Reverse)GAATACTGCCATTTGTACTGCTG4750 - 4772IN
    PAN2R (Reverse)CTGCCATCTGTTTTCCATAYTC5037 - 5058IN

    Table 9. Details of sequencing primers.

    8.7.

    Label 96-well plate for the cycle sequencing reaction PCR.

    8.8.

    Dispense 9µL of each primer mix into the respective wells of a 96-well plate.

    8.9.

    Add 1µL purified amplicons to the respective wells.

    Note
    It is recommended to add the eight primers across the plate (e.g. primer RTC1F in wells A1 - A12), with samples added in plate columns (e.g. sample 1 in wells A1 - H1).

    CAPILLARY ELECTROPHORESIS

    9.

    Capillary electrophoresis on 3730 Genetic Analyzer

    9.1.

    Setup plate run on Genetic Analyzer (Applied Biosystems), according to cycle sequencing reaction plate layout.

    9.2.

    Load plate onto Genetic Analyzer (Applied Biosystems) and start capillary electrophoresis run.

    9.3.

    At the end of the run, remove the plate from the Genetic Analyzer and dispose in biohazard waste.

    9.4.

    Login to SeqA6 software on a computer connected to the Genetic Analyzer and run primary analysis.

    9.5.

    Save the analyzed data files, and copy the ab1 sequence files to USB disk.

    SEQUENCE ANALYSIS

    10.

    Sequence editing and drug resistance interpretation.

    10.1.

    Upload ab1 sequence files from USB key into Geneious software (Biomatters Ltd, New Zealand).

    10.2.

    Trim and edit sequences for good quality reads.

    Note
    If you are in the correct reading frame, the beginning of protease gene should start with the amino acids PQITLW, the beginning of reverse transcriptase gene should start with PISPIE, and the beginning of integrase gene should start with FLDGID.

    10.3.

    Align all sequence files for each sample to an annotated HIV reference sequence, and edit sequences where necessary. This entails identifying any ambiguities, and verifying positions with mixed bases by inspecting quality (symmetry, height, and background) of the base calls.

    10.4.

    Align all consensus sequences and perform phylogenetic tree reconstruction to assess sequence similarity.

    Note
    If any two sequences have >97% similarity, all the stages of the protocol should be reviewed, starting with sequence analysis and going back to RNA extraction, to ensure that there was no sample mix up (i.e. sample switching, mislabeling), or contamination.

    10.5.

    Export consensus sequences in FASTA format and assess HIV drug resistance mutations using the Stanford University HIV drug resistance database (http://hivdb.stanford.edu/hivdb/by-sequences/).

    BIGDYE CYCLE SEQUENCING v3.1

    110.
    • The following procedure is used to set up the sequencing reaction mix using the BigDye Terminator v3.1 cycle sequencing kit (LifeTechnologies) and 8 primers per sample.

    • Thaw all reagents at room temperature.

    • Label 1.5mL tubes, one for each primer mix.

    • Vortex sequencing buffer and primers and briefly spin to bring the contents to the bottom of the tube.

    • Mix BigDye by tapping tube and briefly spin to bring the contents to the bottom of the tube.

    • Prepare master mix for each primer as shown in Table 4.

    ABC
    ReagentVolume per reaction (µl)Concentration per reaction
    PCR grade water6.1-
    5X Sequencing buffer21.1X
    Primer (3.2µM)0.50.2µM
    BigDye Sequencing mix0.4-
    Total9.0-

    Table 6 Sequencing reaction mix for each sequencing primer

    ABCD
    Primer (Direction)Primer sequenceHXB2Gene
    RTC1F (Forward)ACCTACACCTGTCAACATAATTG2486 - 2508PR and RT
    RTC2R (Reverse)TGTCAATGGCCATTGTTTAACCTTTGG2630 - 2604PR and RT
    RTC3F (Forward)CACCAGGGATTAGATATCAATATAATGTGC2965 - 2994PR and RT
    RTC4R (Reverse)CTAAATCAGATCCTACATACAAGTCATCC3101 - 3129PR and RT
    KVL076 (Forward)GCACAYAAAGGRATTGGAGGAAATGAAC4161 - 4188IN
    KVL082 (Forward)GGVATTCCCTACAATCCCCAAAG4647 - 4669IN
    KVL083 (Reverse)GAATACTGCCATTTGTACTGCTG4750 - 4772IN
    PAN2R (Reverse)CTGCCATCTGTTTTCCATAYTC5037 - 5058IN
    Optional primers
    2586F (Forward)AAGCCAGGAATGGATGGCCCA2586 - 2606PR and RT
    2713R (Reverse)GGATTTTCAGGCCCAATTTTTG2713 - 2692PR and RT
    PAN3F (Forward)TTAAAAGAAAAGGGGGGATTGGG4783 - 4805IN
    KVL084 (Reverse)TCCTGTATGCARACCCCAATATG5243 - 5265IN

    Table 7 Sequencing primers for complete HIV-1 PR, RT and IN sequencing.

    • Label 96 well plate for the sequencing reaction PCR.

    • Dispense9µL of each mix into the respective wells in a 96 well plate.

    • Add 1µL purified amplicons to the respective wells.

    Note: Note: It is recommended to use the plate layout on the worksheet for cycle sequencing reaction and sequencing reaction purification.

    • Details of the sequencing primers are shown in table 7.

      BigDye XTerminator Purification

    Note: Note: Remove SAM and XTerminator reagents from fridge and equilibrate to room temperature prior to preparing SAM/BigDye XTerminator solution

    • Centrifuge the reaction plate for 1 minute following the sequencing reaction.

    • Ensure that the XTerminator solution is homogenized by vortexing thoroughly.

    • Vortex the bottle of BigDye XTerminator beads for 0h 0m 8s to 0h 0m 10s before mixing with the SAM solution.

    • Prepare the SAM/BigDye XTerminator bead working solution (as shown in Table 11) in a 50mLFalcon tube.

    ABC
    ComponentVolume per 10μl reactionVolume (µl) x n
    SAM solution45μL
    BigDye XTerminator bead solution10μL
    Total volume55μL

    Table 8 SAM/BigDye XTerminator solution

    • Mix the SAM/BigDye XTerminator bead working solution thoroughly by vortexing and dispense in a reagent reservoir.

    • Remove the PCR septa mat and add the required volume (55µL/ 110µL) of SAM/BigDye XTerminator bead working solution using a multi-channel pipette.

    • Seal the plate using an aluminium plate seal.

    • Vortex the plate on a plate shaker at 1800rpm for 0h 30m 0s

    • Centrifuge the plate at 4000rpmfor 0h 4m 0s

    • Sequence samples on an ABI 3730 Genetic Analyzer (Applied Biosystems, Foster City, United States)

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