The short answer: these are control probesets, derived from E.coli sequences.
The longer answer - there are two good sources of documentation for Affymetrix arrays. The first is the Affymetrix website; here is the product page for the U95 set. You'll need to create a (free) account to access files.
The second is NCBI GEO - start with the platforms page and search for "u95a". Result. Scroll down and download the full data table, which is a delimited text file that you can explore:
grep AFFX-BioC-5_at GPL91-39600.txt
AFFX-BioC-5_at --Control Homo sapiens Mar 11, 2009 Control sequence GenBank J04423 E coli bioC protein (-5 and -3 represent transcript regions 5 prime and 3 prime respectively) J04423 0008152 // metabolic process // inferred from electronic annotation /// 0009058 // biosynthetic process // inferred from electronic annotation /// 0009102 // biotin biosynthetic process // inferred from electronic annotation /// 0009236 // cobalamin biosynthetic process // inferred from electronic annotation 0005737 // cytoplasm // inferred from electronic annotation 0000166 // nucleotide binding // inferred from electronic annotation /// 0000287 // magnesium ion binding // inferred from electronic annotation /// 0003824 // catalytic activity // inferred from electronic annotation /// 0004015 // adenosylmethionine-8-amino-7-oxononanoate transaminase activity // inferred from electronic annotation /// 0004076 // biotin synthase activity // inferred from electronic annotation /// 0004141 // dethiobiotin synthase activity // inferred from electronic annotation /// 0005506 // iron ion binding // inferred from electronic annotation /// 0005524 // ATP binding // inferred from electronic annotation /// 0008168 // methyltransferase activity // inferred from electronic annotation /// 0008483 // transaminase activity // inferred from electronic annotation /// 0008710 // 8-amino-7-oxononanoate synthase activity // inferred from electronic annotation /// 0016740 // transferase activity // inferred from electronic annotation /// 0016769 // transferase activity, transferring nitrogenous groups // inferred from electronic annotation /// 0016874 // ligase activity // inferred from electronic annotation /// 0030170 // pyridoxal phosphate binding // inferred from electronic annotation /// 0042242 // cobyrinic acid a,c-diamide synthase activity // inferred from electronic annotation /// 0046872 // metal ion binding // inferred from electronic annotation /// 0051536 // iron-sulfur cluster binding // inferred from electronic annotation /// 0051537 // 2 iron, 2 sulfur cluster binding // inferred from electronic annotation /// 0051539 // 4 iron, 4 sulfur cluster binding // inferred from electronic annotation
