GreA in each Bacillus subtilis cell, which is nearly twice that of RNAP levels and far more than that of other transcription factors. The distribution of highly concentrated GreA molecules in the cell may engender an effective chaperone buffer like DnaK and other chaperones. In turn, this would help to prevent protein aggregation, promote renaturation of denatured proteins, and thus enhance cellular resistance to stress. Our result that the temperature sensitive greA/greB double mutant strain suffers more extensive protein aggregation suggests that GreA may act as chaperone in vivo. Increased expression of GreA under acidic stress and the enhanced heat-shock survival rate of the GreAoverexpressing strain provide extra evidence for such activity. Deletion of greA results in PR-171 sensitivity to salt stress and double-deletion of greA and greB causes heat sensitivity, which suggest that GreA plays a critical role in stress resistance. Owing to the chaperone activity of GreA, we infer that GreA may protect or stabilize RNAP in stressful conditions. If this is one of the major roles of GreA, we predict that RNAP should be one of its natural substrates. We further propose that GreA may play a novel role in the transcription apparatus. Interestingly, the Database of Interaction Protein shows that GreA interacts directly with ribosome subunits, such as DnaK, DnaJ, GroES, ClpX, and other chaperones in vivo, suggesting the existence of potentially important relationships between GreA and the molecular chaperone system. In conclusion, this study may provide the first evidence that indicates a link between the transcription apparatus and protein quality control. CC is a slow-growing but highly metastatic tumor, which is often detected at an unresectable stage; therefore, most patients have a poor prognosis with a median survival of 6–12 months. CC is insensitive to chemotherapy, immunotherapy, radiotherapy and other adjuvant treatments, and curative surgical resection is currently the only effective therapy, with an overall 5-year survival rate of 40%. However, more than a third of patients with CC are unsuitable candidates for curative resection, as the disease is usually detected at an advanced stage. Hence, new methods of early diagnosis are urgently required in order to improve the treatment and prognosis of CC patients. Currently, the clinical diagnosis of CC relies on computed tomography or B type ultrasonography examinations which have a poor sensitivity, especially for the detection of small lesions with a hilar localization. In addition, brush cytology via endoscopy has a sensitivity of 50% for the early diagnosis of CC, which is attributed to the high desmoplastic nature of this disease. The serum biomarker CA 19-9 is commonly used for the diagnosis of CC; however, CA 19-9 has low sensitivity of 50–60% and specificity of 80%. Therefore, improved fluid-based biomarkers are urgently required to enable the early diagnosis of CC, and additional insight on the pathogenesis of this disease is critical in order to identify new potential therapeutic strategies. Proteomics is the most commonly used technology for the identification of disease-specific biomarkers. The protein expression profiles of normal cells undergo distinct changes during malignant transformation, which may potentially provide appropriate biomarkers. In CC in bile than serum, and may therefore be easier to identify in bile. Although a few studies have attempted to perform large-scale identification of differently expressed.