from other infected people, then it can be assumed that they were all infected from a
common source. Thus by comparing their eating habits, food sources, etc. the source
of the infection can be traced to a restaurant, food item, etc. Figure 10.15 shows the
restriction patterns from different strains ofNeisseria meningitidis.10.4.4 Electrophoresis of RNA
Like that of DNA, electrophoresis of RNA is usually carried out in agarose gels, and the
principle of the separation, based on size, is the same. Often one requires a rapid
method for checking the integrity of RNA immediately following extraction but
before deciding whether to process it further. This can be achieved easily by electro-
phoresis in a 2% agarose gel in about 1 h. Ribosomal RNAs (18 S and 28 S) are clearlyFig. 10.15PFGE separation of the digestion pattern produced with the restriction enzyme Nhe1, of 21 strains of
Neisseria meningitidis. There are two molecular weight marker tracks at either end of the gel. (Courtesy of
Dr Giovanna Morelli, Max-Planck Institute for Molecular Genetics, Berlin, Germany.)426 Electrophoretic techniques