Table 1. 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.
| Motif | KKXK | KKXR | KRXK | KRXR | RRXR | RRXK | RXKR | RKXK | OFa | MFb | OF/MF |
| Res. X | |||||||||||
| G | 4.84 | - | - | - | - | - | - | - | 4.84 | 7.4 | 0.65 |
| A | 1.61 | - | - | - | - | - | - | - | 1.61 | 7.4 | 0.22 |
| V | 1.61 | - | - | - | - | - | - | - | 1.61 | 6.8 | 0.24 |
| L | 3.23 | - | - | - | - | - | 1.61 | - | 4.84 | 7.6 | 0.64 |
| I | - | - | - | 1.61 | - | - | - | - | 1.61 | 3.8 | 0.42 |
| P | 3.23 | - | - | 1.61 | 4.84 | - | - | - | 9.68 | 5.0 | 1.94 |
| S | - | - | 1.61 | 1.61 | 3.23 | - | - | - | 6.45 | 8.1 | 0.8 |
| T | 1.61 | - | - | - | - | - | - | - | 1.61 | 6.2 | 0.26 |
| C | - | - | - | - | - | - | - | - | 0.00 | 3.3 | 0.00 |
| M | - | - | - | - | - | 1.61 | - | - | 1.61 | 1.8 | 0.90 |
| N | 6.65 | - | 1.61 | 3.23 | 6.45 | - | - | - | 17.74 | 4.4 | 4.03 |
| Q | - | 1.61 | - | - | 3.23 | - | - | - | 4.84 | 3.7 | 1.31 |
| F | - | - | - | - | 1.61 | 1.61 | - | - | 3.23 | 4.0 | 0.81 |
| Y | - | - | - | - | - | - | - | - | 0.00 | 3.3 | 0.00 |
| W | - | - | - | - | 1.61 | - | - | - | 1.61 | 1.3 | 1.24 |
| D | - | - | - | - | - | - | - | - | 0.00 | 5.9 | 0.00 |
| E | - | - | - | - | - | - | - | - | 0.00 | 5.8 | 0.00 |
| K | 6.45 | 4.84 | - | - | 3.23 | - | 1.61 | - | 16.13 | 7.2 | 2.24 |
| R | - | 3.23 | 1.61 | - | 17.74 | - | - | - | 22.60 | 4.2 | 5.38 |
| H | - | - | - | - | - | - | - | - | 0.00 | 2.9 | 0.00 |
| 29.03 | 9.68 | 4.84 | 8.06 | 41.93 | 3.23 | 3.23 | 0.00 | ||||
| 51.61 | 48.39 | ||||||||||
a
Among 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.
b
Mean frequency (MF) of each aminoacid observed in vertebrate proteins.