The discovery of the importance of long uninterrupted perfect matches and the long-range effects of mismatch (see 'Results' section), which are not embodied in current NN hybridization theories (19) , led us to formulate a simple new descriptive theory. The new algorithm includes aspects of NN theory (8, (20) (21) (22) but extends this to longer hybridizing segments and includes the effects of dInosine in the long oligonucleotides. Visual Omp TM 7.0 predicted that some 70-mer combinations would not hybridize, yet they did hybridize. In order to better predict hybridization, we investigated predictive strategies that took into account the matching nt, its neighbors, the length of the matching region, and the cooperativity of neighboring matching regions. We finally settled for an algorithm which attempts to model the nucleation and zipping stages during the hybridization process. The new model was termed NucZip ( Figure 5B ). The results obtained using this model was then correlated with those obtained using Visual OMP TM 7.0 and both were compared with experimental data.