I got smeared bands after the isolation of genomic DNA from a plant. I treated the samples with RNAse A, but again smeared bands appeared, though less visible (Media attached). What could be the reason?
What you see in the gel is semi-degraded genomic DNA. Hence no effect of RNAse treatment is visible. If your DNA was visibly contaminated with RNA, you would see rRNAs as distinct bands; mRNA would be likely invisible. When DNA is prepared correctly, it migrates as a >20 kb band - it is still in fragments but not smeared.
However, if you need the genomic DNA e. g. for PCR, its smeared appearance is of no concern as long as you have enough fragments in it that contain the region of interest.
You should check the suitability of your RNase: take a known good sample of DNA (any previously isolated good DNA, plasmid or PCR product), place one sample with your RNase and one sample without RNase. Incubate at room temperature for 20-30 minutes. If the sample without RNase remains unchanged and the other one smears, then your RNase is contaminated with DNase. If so, heat your RNase at 90-1000C for 1 hour in a water bath or use a thermocycler.
Thank you Libor Krásný and Irina Mikhailovna Zyrianova for your valuable responses. I have learned a lot and will apply your suggestions.
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