What does the "_x_at" extension represent in the HG-U133 probe set name?
Occasionally, it is not possible to select either a unique probe set or a probe set with all probes common among multiple transcripts ("_s_at" ). In such cases, similarity criteria are suspended, and the resulting probe set name is appended with the "_x_at" extension. These probe sets contain some probes that are identical, or highly similar, to unrelated sequences. These probes may cross-hybridize in an unpredictable manner with sequences other than the main target. Data generated from these probe sets should be interpreted with caution, due to the likelihood that some of the signal is from transcripts other than the one being intentionally measured.
The following is an illustration of the relationship between "_x_at" group members: