Single-atom substitution experiments provide atomic resolution biochemical
information concerning RNA structure and function, Traditionally, these exp
eriments are performed using chimeric RNAs generated by reassembly of full-
length RNA from a synthetic substituted oligonucleotide and a truncated RNA
transcript, Unfortunately, this technique is limited by the technical diff
iculty of assembling and measuring the effect of each singly substituted mo
lecule in a given RNA, Here we review an alternate method for rapidly scree
ning the effect of chemical group substitutions on RNA function. Nucleotide
analog interference mapping is a chemogenetic approach that utilizes a ser
ies 5'-O-(1-thio)-nucleoside analog triphosphates to simultaneously, yet in
dividually, probe the contribution of a functional group at every nucleotid
e position in an RNA molecule. A population of randomly substituted RNAs is
prepared by including phosphorothioate-tagged nucleotide analogs in an in
vitro transcription reaction. The active molecules in the RNA population ar
e selected by an activity assay, and the location of the analog substitutio
n detrimental to activity is identified by cleavage at the phosphorothioate
tag with iodine and resolution of the cleavage fragments by gel electropho
resis, This method, which is as easy as RNA sequencing, is applicable to an
y RNA that can be transcribed in vitro and has an assayable function. Here
we describe protocols for the synthesis of phosphorothioate-tagged analogs
and their incorporation into RNA transcripts, The incorporation properties
and unique biochemical signatures of each individual analog are discussed.
(C) 1999 Academic Press.