Northern blotting principles

This procedure is similar in principle to Southern and Northern blots, but it is designed for the transfer of proteins from gels onto nitrocellulose membranes. An electrophoretic technique is often used to speed the transfer by 10-fold, and the apparatus used for such Western transfers is shown in Figure 9.15. The rapid electrophoretic process ensures that complete transfer occurs with minimal diffusional zone broadening. 

Whereas mieroarray analysis of gene expression employs similar steps as Northern blot hybridization, it is radically different in principle. The major difference is that the roles of the nucleie aeid bound to the substrate and the labeled nueleic acid in the hybridization solution are reversed for mieroarrays. In mieroarray analysis, the DNA probe is fixed to the substrate with eaeh spot on the array con-... 

The principle of this analysis is to incorporate biotin-labelled residues in the RNA during transcription, assemble the RNA-pro-tein complexes, fractionate the complexes according to size, and immobilise the RNA within individual fractions on streptavidin beads (see Fig. 4.3). Finally, the nuclear proteins/RNAs are eluted, identified and quantitated by Northern or Western blotting (Fig. 5.4). Although this method was originally designed to analyse the composition of the spliceosome it can be used as a general affinity purification system. 

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