Some arb databases contain accessibility SAIs (like 'E_coli_I_Accessibility').
These SAIs contain information about the FISH probe accessibility to different parts of the molecules of several selected species (Escherichia coli, Pirellula, Metallosphaera sedula, Saccharomyces cerevisiae).
These SAIs contain information about the relative brightness of the fluorescence hybridization signals as determined in .
The determined brightness was assigned to six classes of brightness and was encoded into six different characters in the SAIS:
Brightness Relative Characters
class brightness used in SAIs
I > 0.8 Ee
II 0.6 - 0.8 Ff
III 0.4 - 0.6 Ii
IV 0.2 - 0.4 Oo
V 0.05- 0.2 Pp
VI < 0.05 Xx
Different probe target sites often show different signal strengths, even when these sites overlap. That means the probe accessibility depends on the position of the complete probe and its not possible to provide a reasonable accessibility value for single base positions. Therefore the information has been distributed over several separate SAIs, e.g. for Escherichia coli there are five SAIs (E_coli_I_Accessibility, E_coli_II_Accessibility, ..., E_coli_V_Accessibility).
Uppercase characters in the SAI mark the endpoints of single probe sequences, whereas lowercase characters are used for inner positions.