N4-Acetylcytidine. A previously unidentified labile component of the small subunit of eukaryotic ribosomes.

The nucleoside content of 18 S rRNA from rat liver is determined under conditions known to prevent the destruction of chemically labile modified nucleosides. Two base-modified nucleosides, not completely identified before, are shown to be N6-methyladenosine and 7-methylguanosine. The results further demonstrate the presence of a hitherto unidentified component of 18 S rRNA whose spectra and chromatographic properties are identical with that of N4-acetylcytidine. In addition, this compound is not detectable in 28 S rRNA nor in 16 S rRNA derived from the small ribosomal subunit of Escherichia coli. However, it appears to be conserved in the small ribosomal subunit of eukaryotes, since it is also present in yeast 17 S rRNA and chicken liver 18 S rRNA.