Occurrence frequencies (%) of possible NoLS sequences (K/R-K/R-X-K/R) and of the twenty aminoacids at the X position in several NoLS-containing nucleolar proteins.

aAmong the eight possible sequence combinations (upper line), observed frequency (OF) of each aminoacid at the X position in NoLS present in 61 well-characterized nucleolar proteins and using for the analysis.bMean frequency (MF) of each aminoacid observed in vertebrate proteins.