If you want to prepare a good quality of RNA for your experiments such as real-time PCR, it is necessary to do DNAse treatment. However, you can use the RNA for semiquantitative PCR when your 260/280 and 260/230 values are fine. 

It would also be ideal to check the RNA quality using formaldehyde agarose gel electrophoresis.

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I've always found that if your PCR primers span an exon boundary, DNase treatment isn't necessary. Although I work in mammals and introns are quite large. Not sure about your organisms. When looking at lowly expressed RNAs by PCR that don't have exons, there's really no way around it. If you're doing some assay that uses an RNA ligase, again DNAse isn't really necessary as the ligase is highly specific to RNA. Depends on your assay. Alternatively, if you do a oligo dT purification, DNA contamination is usually negligible. 

I have found DNAse treatment to usually be unnecessary and since it's not that cheap, I skip it. If you are doing qRTPCR, i definitely agree with Jacob that your primers should span an intron and that should help eliminate DNA contamination problems. 

You can also test to see if you are getting DNA contamination in your RNA in this way:

1 - Make cDNA from your RNA, and include a reaction that contains everything it should normally except reverse transcriptase.

2 - In a control well or wells, set up a qRT-PCR reaction with the 'cDNA' sample that did not contain any reverse transcriptase.

You should not see any PCR amplified from that sample.

If you do, its because the PCR was working off of genomic DNA that was contaminating the RNA sample.

Hi Kunal,

The 260/280 and 260/230 ratios are only a guide to know if your sample is contaminated with proteins (260/280) or organic solvents from the isolation protocol (260/230). Therefore they do not tell you anything about RNA integrity (if RNA is intact or you had degradation).

To check integrity, you can use denaturing formaldehyde gels and check the 28S:18S rRNA ratio. This is the classic method, more recently companies developed machines like Agilent Bioanalyzer that gives you a RIN (RNA integrity number), 10 is perfect and 0 is completely degraded.

Regarding DNase treatment, it depends on what you are going to do after it. If you are going to measure gene expression I would recommend it. It will remove the possibility of DNA contamination that could change your expression values and also would reduce the chance of unspecific amplification.

Best!

Its good to do DNase treatment especially for further downstream applications despite the good 260/280 values. It may not change the results much but it improves the quality of your RNA which gives you more confidence in your results.

1.For checking that your RNA have gDNA contamination you can do a PCR reaction with your RNA template using a primer pairs that amplify gDNA. if you have an amplified DNA bound on agarose gel, surely your RNA contaminate with DNA. however you should have negative and positive controls in this PCR reaction.

2. if you have DNA contamination on your RNA sample you have two ways to prevent the gDNA amplification. first try to design your primer which span an intron (with a lenght more than 1000bp) or design the primers on exon/exon junction region on your template. second way is uses of DNase treatment that I suggest you using the Roch DNase treatment kit for this purpose.

best wishes

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yes

if you want to have a good result you must add it