Hepatitis B virus(HBV)affects approximately two billion people worldwide and more than 240 million people in the world are currently chronic carrier that could develop serious complications in the future,like liver ci...Hepatitis B virus(HBV)affects approximately two billion people worldwide and more than 240 million people in the world are currently chronic carrier that could develop serious complications in the future,like liver cirrhosis and hepatocellular carcinoma.Although an extended HBV immunization program is being carried out since the early‘80s,representing effective preventive measure,leading to a dramatic reduction of HBV hepatitis incidence,globally HBV infection still represents a major public health problem.The HBV virus is a DNA virus belongs to the Hepadnaviridae family.The HBV-DNA is a circular,partial double strand genome.All coding information is on the minus DNA strand and it is organized into four open reading frames.Despite hepatitis B virus is a DNA virus,it has a high mutation rate due to its replicative strategy,that leads to the production of many nonidentical variants at each cycle of replication.In fact,it contains a polymerase without the proofreading activity,and uses an RNA intermediate(pg RNA)during its replication,so error frequencies are comparable to those seen in retroviruses and other RNA viruses rather than in more stable DNA viruses.Due to the low fidelity of the polymerase,the high replication rate and the overlapping reading frames,mutations occur throughout the genome and they have been identified both in the structural and not structural gene.The arise of mutations being to develop of a whole of viral variants called"quasi-species"and the prevalent population,which favors virus replication,was selected by viral fitness,host’s immune pressure and external pressure,i.e.,vaccination or antiviral therapy.Naturally occurring mutations were found both in acute and chronic subjects.In the present review we examine and discuss the most recent available data about HBV genetic variability and its significance.展开更多
Ablotlc stresses, such as drought, high salinity, and cold/freezing, lead plants to produce excess reactive oxygen species. Catalase, a unique hydrogen peroxide-scavenging enzyme, plays a very Important role In plants...Ablotlc stresses, such as drought, high salinity, and cold/freezing, lead plants to produce excess reactive oxygen species. Catalase, a unique hydrogen peroxide-scavenging enzyme, plays a very Important role In plants. To characterize the catalase involved In plant response to ablotlc stresses, we constructed a cDNA library from 4℃-treated Festuca arundinacea Schreb seedlings and isolated a catalase gene from this library. The cDNA （FaCat1, 1 735 bp） contained an open reading frame of 1 479 bp. BLAST analysis Indicated that the deduced amino acid sequence showed 96% Identity with that from wheat TaCat1 and 87% Identity with that from maize ZmCat2. Northern blotting analysis showed an obvious Increase of FaCat1 transcripts In leaves In contrast with roots. Time-course analysis of the expression of FaCat1 in F. arundinacea leaves showed that FaCat1 expression was upregulated in cold- and salt-stressed leaves, with the FaCat1 transcripts accumulat-Ing mostly at 4 or 2 h after cold or salt stress, respectively. No significant changes in FaCat1 transcription were observed in dried leaves and inhibition of FaCat1 transcription was found In absclsic acid （ABA）-treated leaves, Indicating that the FaCat1 gene is differentially expressed during cold, high salt, drought, and ABA treatment In F. arundinacea leaves.展开更多
文摘Hepatitis B virus(HBV)affects approximately two billion people worldwide and more than 240 million people in the world are currently chronic carrier that could develop serious complications in the future,like liver cirrhosis and hepatocellular carcinoma.Although an extended HBV immunization program is being carried out since the early‘80s,representing effective preventive measure,leading to a dramatic reduction of HBV hepatitis incidence,globally HBV infection still represents a major public health problem.The HBV virus is a DNA virus belongs to the Hepadnaviridae family.The HBV-DNA is a circular,partial double strand genome.All coding information is on the minus DNA strand and it is organized into four open reading frames.Despite hepatitis B virus is a DNA virus,it has a high mutation rate due to its replicative strategy,that leads to the production of many nonidentical variants at each cycle of replication.In fact,it contains a polymerase without the proofreading activity,and uses an RNA intermediate(pg RNA)during its replication,so error frequencies are comparable to those seen in retroviruses and other RNA viruses rather than in more stable DNA viruses.Due to the low fidelity of the polymerase,the high replication rate and the overlapping reading frames,mutations occur throughout the genome and they have been identified both in the structural and not structural gene.The arise of mutations being to develop of a whole of viral variants called"quasi-species"and the prevalent population,which favors virus replication,was selected by viral fitness,host’s immune pressure and external pressure,i.e.,vaccination or antiviral therapy.Naturally occurring mutations were found both in acute and chronic subjects.In the present review we examine and discuss the most recent available data about HBV genetic variability and its significance.
文摘Ablotlc stresses, such as drought, high salinity, and cold/freezing, lead plants to produce excess reactive oxygen species. Catalase, a unique hydrogen peroxide-scavenging enzyme, plays a very Important role In plants. To characterize the catalase involved In plant response to ablotlc stresses, we constructed a cDNA library from 4℃-treated Festuca arundinacea Schreb seedlings and isolated a catalase gene from this library. The cDNA （FaCat1, 1 735 bp） contained an open reading frame of 1 479 bp. BLAST analysis Indicated that the deduced amino acid sequence showed 96% Identity with that from wheat TaCat1 and 87% Identity with that from maize ZmCat2. Northern blotting analysis showed an obvious Increase of FaCat1 transcripts In leaves In contrast with roots. Time-course analysis of the expression of FaCat1 in F. arundinacea leaves showed that FaCat1 expression was upregulated in cold- and salt-stressed leaves, with the FaCat1 transcripts accumulat-Ing mostly at 4 or 2 h after cold or salt stress, respectively. No significant changes in FaCat1 transcription were observed in dried leaves and inhibition of FaCat1 transcription was found In absclsic acid （ABA）-treated leaves, Indicating that the FaCat1 gene is differentially expressed during cold, high salt, drought, and ABA treatment In F. arundinacea leaves.
