is specific for complementary sequences a noncomplementary 32 p labelled oligonucleotide x 14 nucleotides long 32 p 5 39 catgcgttcccgtg seq id no 2 did not react with compound 1 7a l pr after addition of 100 mm fluoride for the samples in lanes 5 9 the fluoride concentration was varied from 0 0 250 mm fig4 shows that fluoride is not the only possible triggering agent the signal for inducing reaction is not so much dependent on fluoride as it is dependent on a general increase in ionic strength accordingly silyl containing reactive centers can be used for both in vivo and in vitro uses no other ionic strength dependant covalent binding reagent has ever before been proposed or tested protocol 1 4 synthesis of reactive centers with reactivity similar to compound 1 7a c by treating compound 1 6 with various nucleophiles x a series of related appendages for triggered reaction were produced str14 reactive centers other than those represented by 1 7 have been constructed for inducible and selective crosslinking of the complex formed by a probe l pr and target t str15 protocol for the preparation of a reactive center designed for coupling to an aminolinker probe l pr 3 5 methylbenzoyl propionic acid compound 2 2 as shown in scheme 2 compound 2 2 was prepared by the method of raval et al j univ bombay 7 pt 3 184 1983 ca 33 3779 1989 p cresol 4 0 g 37 mmol and succinic anhydride 3 4 g 34 mmol were combined in 1 1 2 2 tetrachloroethane 40 ml and the mixture was heated to 60 u00b0 c.