It has been suggested that eukaryotic tRNA genes might adopt a higher
order stem and loop structure to facilitate transcription by interacti
on of their variably spaced intragenic promoter blocks. Using sodium b
isulphite, which reacts specifically with cytosine residues in single-
stranded nucleic acids, no deamination of C in the TTCGAA sequence of
the 3' ICR of a tRNA(Leu) gene could be detected under conditions whic
h caused 60% deamination of cytosine residues within the loop region o
f a synthetic cruciform cloned in the same negatively supercoiled plas
mid vector. We conclude that, under these conditions, such structures
occur in tRNA genes very rarely, if at all.