Based on three-dimensional modeling analysis, rt309 is located at the ����turn���� of the helix clamp motif in the thumb domain that interacts with the DNA templateprimer. In this case, rtM309K aa substitution is likely to affect the precise conformation of the two a-helices and their interactions with the DNA template-primer, consequently impairing polymerase activity. The sequence from rt304 to rt311 is highly conserved among genotypes A�CH, and cell transfection experiments indicated that natural or artificial substitutions in this region could drastically decrease the viral replicative competency. Further studies have revealed that the mechanisms for decreased replicative Ogerin negative control competency are mediated by hampering the encapsidation of pgRN. Interestingly, we also observed a significantly lower level of HBV DNA in the patients infected with rtM309K mutant in our study, providing further evidence from patients to support the important role of rt304�C311 in viral replication. However the mechanism underling the association of rtM309K and HCC is not clear. In vitro and in vivo experiments using a 1.36genome-length HBV BAY-678 construct containing rtM309K are needed to explore its biological impact on viral replication. Further, HBV transgenic mice containing RT mutated sequence could help to investigate the role of these mutants in liver carcinogenesis. There are several studies from Asia reported that HBV viremia is associated with increased risk of HCC. However, few studies stratified the DNA level and reported a successively increased OR value of HCC with the viral DNA increasing. In the current study, the patients with middle-high level of serum HBV DNA were most likely to be associated with HCC. Our data are consistent with some recent publications. Interestingly, these studies were all from east China, especially from Qidong area. So far, the explanation for this discrepancy is unclear. Different from other regions of Asia, almost all HBV patients in Qidong are infected with genotype C, which was significantly associated with serum HBV DNA level. Thus, HBV genotype may influence the association between HBV load and HCC risk. Unlike the mutations A799G and T1055A, A987G does not cause an amino acid change in HBV polymerase.