From what kind of alien being did you isolate these RNAs from? :-)

Looks like the rRNAs came from a three subunit ribosome! Either that, or you got a serious bacterial contamination (or a sample with plant rRNAs)! 

If you run total RNA from a mixture of mammalian and bacterial cells, you would see three-four distinct high molecular weight bands in the following order:

28s rRNA (5 kb)

23s rRNA (2.9 kb)

18s rRNA  (1.8 kb)

16s rRNA (1.5 kb)

If you look closely and compare lanes 2-7 with the last lane without extra band, you would notice that the 18srRNA bands in the contaminated lanes are a bit smeared out which could be the bacterial 16s rRNA. If you are planning to try again with new cells from the stock (of cell line or primary cells), make sure you decontaminate your hood/incubator first.

Some single strand RNA virus? Which is the difference with the last samples? There is a laddering may be you have some degradation or DNA contamination, but not in the last sample

I don't think so. These are tumor cell lines, and the last lane (the one that  doesn't have the band) is a SV40-immortalized fibroblast cell. And in this case, no band appeared.

 Why you think that cannot be a DNA contamination? May be the cells were in apoptosis

I'll try amplifying the extracted RNA to see if there is any DNA there, but I believe that's not the case.

From what kind of alien being did you isolate these RNAs from? :-)

Looks like the rRNAs came from a three subunit ribosome! Either that, or you got a serious bacterial contamination (or a sample with plant rRNAs)! 

If you run total RNA from a mixture of mammalian and bacterial cells, you would see three-four distinct high molecular weight bands in the following order:

28s rRNA (5 kb)

23s rRNA (2.9 kb)

18s rRNA  (1.8 kb)

16s rRNA (1.5 kb)

If you look closely and compare lanes 2-7 with the last lane without extra band, you would notice that the 18srRNA bands in the contaminated lanes are a bit smeared out which could be the bacterial 16s rRNA. If you are planning to try again with new cells from the stock (of cell line or primary cells), make sure you decontaminate your hood/incubator first.

Hi, Jonathan. I think your answer is right. I just performed a PCR do detect micoplasm and found out that these RNA from this cell (3 control and 3 treated) are contaminated with it. So I believe I extracted micoplasm RNA too hahaha.

Thank you.

The following characteristics indicate successful RNA preparation:

• For mammalian total RNA, two intensive bands at approximately 4.5 and 1.9 kb should

be observed against a light smear. These bands represent 28S and 18S rRNA. The ratio of

intensities of these bands should be about 1.5-2.5:1. Intact mammalian poly (A)+ RNA

appears as a smear sized from 0.1 to 4-7 (or more) kb with faint 28S and 18S rRNA

bands.

• In the case of RNA from non-mammalian sources (plants, insects, yeast, amphibians), the

normal mRNA smear on the non-denaturing agarose gel may not exceed 2-3 kb.

Moreover, the overwhelming majority of invertebrates have 28s rRNA with a so-called

"hidden break" (Ishikawa, 1977). In some organisms the interaction between the parts of

28s rRNA is rather weak, so the total RNA preparation exhibits a single 18s-like rRNA

for more information check the following link 

http://www-personal.umd.umich.edu/~smtiquia/research/protocols/RNA_analysis_on_non-denaturing_agarose_gel_electrophoresis.pdf