By Levi Clancy for Student Reader on
Northern Blots (aka RNA Blots) determine the size of an mRNA transcript (via gel electrophoresis) as well as its abundance (via a probe with bound radioactive 32P). Although DNA restriction enzymes cannot be used with RNA, fortunately different RNA transcripts are naturally of different lengths (depending on the size and number of exons within a transcribed gene). Unfortunately, these complementary regions in these RNA transcripts can bind together. Thus, only after a quick denaturing strong base rinse can RNA purified from a cell can be separated by size via gel electrophoresis. As in Southern Blots, the a filter is then placed atop the filter. RNA segments transfer to the filter, which is then soaked with single-stranded probes. After rinsing away unbound probes, the filter is viewed under an x-ray lamp. Bound RNA bands shine under x-ray, allowing for transcripts of interest to be detected.