We found that the relative expression of p53 regulated miRNAs significantly differed depending on whether GAS5-derived snoRNAs or alternative housekeeping genes such as U6 snRNA or U19 snoRNA were used to normalise results. This implies that the use of the GAS5-derived snoRNAs as normalising genes in the context of DNA damage experiments would lead to an inaccurate interpretation of the results, and suggests that the snRNA U6 or snoRNA U19 would be more appropriate for normalisation in such experiments.This is in keeping with the findings of others who have shown that in experiments involving human tumour samples, snoRNA expression was as variable as miRNA expression and that normalising miRNA PCR expression data to these snoRNAs introduced bias in associations between miRNAs and outcome. The primary virulence factor of STEC is Shiga toxin, which belongs to the AB5 group of toxins. The A-subunit is responsible for inhibiting protein synthesis of the target cells by cleaving the N-glycosidic bond of adenine 4324 in 28S rRNA and preventing tRNA binding. The A-subunit is non-covalently attached to a pentamer of identical B-subunits, which bind to host cell surface receptors mediating cytoplasmic delivery of the Asubunit. Stx includes two immunologically distinct isoforms, Stx1 and Stx2, which share about 60% amino acid identity and a highly conserved general structure. Stx2 is further subtyped into 8 variants, which display approximately 90% amino acid identity. In spite of the high NQ 301 structural similarity, these variants significantly differ in toxicity, with Stx2a being over 100-fold more toxic to mice than Stx1, and variant isoform Stx2b. STEC strains can express one or more Stx variants. However, strains producing Stx2a, Stx2c and Stx2d are more commonly associated with HUS in humans than those producing Stx1 or Stx2b. Previously, in cell free in-vitro translation inhibition assays A-subunits of Stx variants displayed similar activities. This L-733,060 hydrochloride suggested that the enzymatic activities of A-subunits are not likely responsible for the toxicity differences between Stx variants. On the contrary, Stx B-subunits have been shown to display differences in receptor recognition, and influence cellular toxicity. The B-subunits of Stx recognize cell surface glycolipid globotriaosylceramide and to a lesser extent globotetraosylceramide as receptors. Gb3 is composed of a tri-saccharide, called Pk trisaccharide, which is attached to the lipid, ceramide.