RNA Extraction Using the Direct-zol RNA MiniPrep Kit: A Step-by-Step Guide

 

Direct-zol Miniprep workflow for RNAlater samples

After more than 20 years at the bench, I’ve extracted RNA using just about every approach imaginable. I’ve worked with TRIzol, as well as column-based kits from manufacturers such as Qiagen and Invitrogen’s PureLink range. Each method has its merits, but if there’s one thing I’ve learnt, it’s that RNA extraction is as much about choosing your battles as it is about getting a good yield.

In my experience, TRIzol has often delivered the highest RNA yields. The catch? Chloroform. It’s an effective part of the extraction process, but it brings its own set of headaches: working with a hazardous solvent, handling the waste, and making sure everything is disposed of properly. The RNA might be precious, but the waste certainly isn’t something you want accumulating in the corner of the lab!

Column-based kits offer a cleaner, more straightforward workflow, although yields can sometimes be lower than with TRIzol, depending on the sample and extraction conditions.

So, where does that leave us? Somewhere between the old-school chemistry of TRIzol and the convenience of spin columns lies the Direct-zol RNA MiniPrep Kit from Zymo Research. 

It offers an appealing middle ground by combining TRIzol-type sample lysis with column-based RNA purification, without requiring the usual chloroform extraction step.

You'll need

Kit

• Zymo Research Direct-zol RNA Miniprep

R2050 — 50 preps, no TRI Reagent

R2051 — 50 preps, includes 50 mL TRI Reagent

R2052 — 200 preps, no TRI Reagent

R2053 — 200 preps, includes 200 mL TRI Reagent.

If you don't already have TRI Reagent For your experiment, R2051 is the convenient choice.

You'll also need:

• RNase-free microcentrifuge tubes

• RNase-free pipette tips

• microcentrifuge capable of 10,000–16,000 × g

• vortex

• 95–100% ethanol

• appropriate PPE/fume hood for handling TRI Reagent

Part 1 — Prepare the buffers

Do this before starting the samples.

Direct-zol RNA PreWash

Add:

1. 10 mL 95–100% ethanol to the 40 mL PreWash concentrate.

Mix thoroughly.

RNA Wash Buffer

Add:

2. 48 mL 100% ethanol to the 12 mL RNA Wash Buffer concentrate.

Alternatively, the manufacturer's protocol permits 52 mL of 95% ethanol.

DNase I

The kit's lyophilised DNase I is reconstituted with:

3. 275 µL DNase/RNase-free water

for the 1,500-U preparation.

Mix gently by inversion rather than vigorous vortexing and prepare frozen aliquots according to the manufacturer's instructions.

Part 2 — Deal with the RNAlater sample

Step 1 — Recover the cellular pellet

The RNAlater aliquots contain preserved parasite/RBC pellet.

a) Centrifuge the sample at up to 5,000 × g to pellet the cellular material.

Zymo recommends removing the RNAlater supernatant before proceeding.

Step 2 — Remove RNAlater

b) Carefully aspirate the RNAlater supernatant.

• Try to remove as much as possible without disturbing the pellet.

Step 3 — Do not wash unnecessarily

You do not need to automatically introduce a PBS wash at this stage. Every additional wash/pellet is an opportunity to lose material, which is exactly what we don't want.

Zymo's recommended RNAlater approach is simply:

pellet → remove RNAlater → lyse the pellet in TRI Reagent.

Part 3 — TRI Reagent lysis

With the TRI reagent,  we're effectively using the liquid extraction chemistry, but without the phenol/chloroform phase separation.

Step 4 — Add TRI Reagent

Resuspend the pellet thoroughly in an appropriate volume of TRI Reagent.

The Zymo protocol's cell guidance uses approximately:

• ≤10⁵ cells → ≥100 µL TRI Reagent

• ≤10⁶ cells → ≥300 µL

• ≤5 × 10⁶ cells → ≥600 µL.

Do not blindly apply the cell-number table; the practical objective is to completely lyse and homogenise the pellet. Use a needle and syringe to suction the cells up-and-down, if needed.

If the lysate remains very viscous or contains obvious particulate material, Zymo recommends increasing the TRI Reagent volume until the lysate is properly homogenised.

Step 5 — Homogenise thoroughly

1. Vortex/mix until the pellet is completely disrupted.

You don't want visible clumps before proceeding. This is especially important because incomplete lysis is one of the manufacturer's identified causes of poor recovery/viscous lysates.

Part 4 — Direct-zol binding

This is where the workflow becomes much nicer than conventional TRIzol extraction.

Step 6 — Add an equal volume of ethanol

Take your homogenised sample in TRI Reagent.

1. Add: 1 volume 95–100% ethanol to: 1 volume TRI Reagent lysate

Example:

400 µL lysate + 400 µL ethanol

Mix thoroughly.

You do not need to perform chloroform extraction. That's the key advantage of Direct-zol. The manufacturer specifically instructs you to add ethanol directly to the TRI Reagent lysate and load it onto the column.

Part 5 — Load the Zymo column

Step 7 — Load

1. Transfer the lysate/ethanol mixture to a Zymo-Spin IICR Column in its collection tube.

2. Centrifuge at: 10,000–16,000 × g for 30 seconds according to the current protocol.

If your sample exceeds the column's loading volume, load it in successive portions.

The manufacturer specifically notes that samples >700 µL need to be reloaded and centrifuged again.

Transfer the column to a fresh collection tube. Discard the flow-through.

Part 6 — DNase treatment

Step 8 — First wash

1. Add: 400 µL Direct-zol RNA Wash Buffer

to the column.

2. Centrifuge.

3. Discard flow-through.

Step 9 — DNase

Prepare:

• 5 µL DNase I

• 75 µL DNA Digestion Buffer

Prepare a mastermix depending on the no. of samples you are extracting from.

Example

Samples	DNase I	DNA Digestion Buffer	For excess vol. (10% extra)
2	10	75	11ul DNase I + 82.5 buffer
3	15	150	16.5ul DNase I + 165 buffer
4	20	225	22ul DNase I + 247.5 buffer
5	25	300	27.5ul + 330ul buffer

Mix gently.

Apply the entire 80 µL mixture directly to the centre of the column membrane.

Step 10 — Incubate

1. Incubate: 15 minutes at room temperature (20–30°C).

This is the manufacturer's recommended on-column DNase treatment.

Part 7 — Wash

Step 11 — PreWash

1. Add: 400 µL Direct-zol RNA PreWash

2. Centrifuge.

3. Discard flow-through.

Repeat:

4. 400 µL PreWash

5. Centrifuge again.

Step 12 — RNA Wash Buffer

1. Add: 700 µL RNA Wash Buffer

2. Centrifuge for: 1 minute at 10,000–16,000 × g.

This centrifugation ensures removal of residual wash buffer.

Part 8 — Elute

Step 13 — Transfer column

1. Move the column into a clean RNase-free tube.

Step 14 — Elute

1. Add: 50 µL DNase/RNase-free water directly to the centre of the membrane.

2. Centrifuge.

That gives you your RNA.

Zymo permits an elution volume of ≥25 µL if you want a more concentrated preparation.

It’s a good idea to use 30–50 µL initially.

If you have samples that contain very little RNA, go for recovery over maximum concentration unless the RNA yield proves to be extremely low.

You can always concentrate RNA later.