The reaction of an organomercury compound with a nucleoside phosphorothioate: Implications for the prospect of electron microscopic nucleic acid sequencing

Abstract

The proposal of determining nucleic acid sequences by base-specific labelmg with heavy elements and subsequent electron macroscopic observation has been formulated [ 11, but has not been put mto practice. It is generally considered that two types of problems must be resolved before this can be done. (1) A method must be avarlable for labeling each of the four bases wrth high specificity. (ii) Electron mrcroscopists must be able to locate single atoms or clusters of atoms with sufficient confidence. We are concerned here with the former of the two problems. The original approach consrsted m a search for base-specific reactions of nucleic acids wrth electron-dense reagents [2], but rt has proven difficult to modify one out of four bases exclusively and quantrtatrvely. An alternative approach is to introduce the label by m vrtro enzymatic replication or transcription of the nucleic acid using one heavy element-modified and three unmodified nucleosrde trrphosphates as substrates. Mercurated pynmrdme nucleotides were proposed for thus purpose [3] but proved not to be stable enough [4]. Nucleoside 5’-041 throtriphosphates) was used [5] as modrfied buildmg blocks for the m vitro syntheses. The sequence-specific label 1s obtained by reaction of a terpyndme platmum salt