A damage is a general event in the life of cells and may lead to mutation,cancer,and cell/organ death. DNA damage occurring in different phases of cell cycle can activate different damage checkpoint pathways to halt the progress of cell cycle in order to provide time for DNA damage repair. If DNA damage cannot be repaired,cellular apoptosis may be induced. Therefore,DNA damage checkpoint is of great significance for cell survival after DNA damage. This article summarizes recent research on DNA damage responses, including DNA damage checkpoint, DNA damage repair, transcriptional response, and cell apoptosis. We focus on how the DNA damage checkpoint pathway is activated after DNA damage,as well as the functional mechanism of the DNA damage checkpoint pathway. The review aims to help readers understand the great significance of DNA damage checkpoint pathway, providing a theoretical basis for its application in radiotherapy and chemotherapy for cancer.

Objective: To investigate hepatitis C virus(HCV)genotyping and the serum HCV-RNA concentration in patients infected with different HCV genotypes and to provide information for evaluation of disease condition and anti-viral treatment efficacy. Methods: A total of 60 anti-HCV positive serum samples were collected before antiviral treatment. RT-PCR was performed for the 5′ non-cording region and was followed by nucleotide sequencing for HCV genotyping. Meanwhile, serum HCV-RNA concentration was detected by quantitative PCR. SPSS21.0 and Graphpad Prism 5.0 software were used for data analysis. Analysis of variance (ANOVA) was used for comparison among multi-groups and the t-test was used for comparison between two groups. Results: The frequencies of HCV genotypes 1b, 3a, 1a and 2a were 48.3% (29/60), 23.3% (14/60), 16.7% (10/60) and 10% (6/60), respectively. And, there is one subtype 2c was detected in this study. The mean serum viral concentration with standard deviation of HCV in genotype 1a, 1b, 2a, and 3 a were 5.46±1.19, 6.22±0.78, 5.47±0.65, and 5.38±0.98 log₁₀ (IU/ml) respectively. Conclusions The infection rate of HCV genotype 1 was significantly higher than that of genotype 2 and 3 (P<0.01). The statistical analysis showed the serum HCV-RNA concentration in patients with subtype 1b was significantly higher than that of the subtype group 1 a, 2 a, and 3 a (P<0.05). The study of the relationship between HCV genotypes and the serum HCV-RNA concentration may contribute to anti-viral treatment prescription for hepatitis C patients.