生物化学原理教学（杨荣武）Chapter38 Genomic RNA replication.pptVIP

Outline RNA-dependent RNA Replication RNA replication of dsRNA virus RNA replication of ssRNA virus DNA-mediated RNA replication RNA replication of retro-viruses Retro-transposon Retro-transcription catalyzed by telomerase Retro-transcription in the lifecycle of some DNA viruses Retro-transcription occurring in the prokaryotes RNA-dependent RNA Replication RNA-dependent RNA replicase (RdRP) is encoded by viral genomic RNA Proceeds only in 5′→3′ Primers are seldom required Error-prone and highly mutagenic Insensitive actinomycin D and sensitive to RNase Mainly occurs in the cytoplasm of host cells RNA replication of retro-viruses Discovery Retro-viruses 1) Structure 2) Life-cycle (taking HIV as an example)- 3) Retro-transcriptase and its inhibitor Three enzymatic activities Inhibitors: AZT and others 4) “Cocktail therapy” Retro-transcriptase and Its application Discovery of Retro-transcription 1960s: Howard Temin knew that retrovirus genomes were composed of RNA and observed that replication was inhibited by actinomycin D therefore he proposed the concept of reverse transcription ( The Nobel prize awarded to Baltimore and Temin, 1975 ). 1970: Temin and David Baltimore (separately) discovered the RNA-directed DNA polymerase - reverse trascriptase Retroviruses and oncogenes All RNA tumor viruses are retroviruses. RNA virus oncogenes are altered forms of normal host genes that occur in the virus genome. Examples of retroviruses include: Rous sarcoma virus (RSV) Feline leukemia virus Mouse mammary tumor virus Human immunodeficiency virus (HIV) Retroviral Genomic RNA Identical to full-length viral mRNA: 5-m7GpppN cap structure 3-polyA splicing signals U: unique, e.g., U5 is unique to 5-end of the RNA genome Cis-acting signals for replication: R is a direct linear repeat required for strand transfer PBS: primer binding site for first strand synthesis PPT: polypurine tract primes second strand synthesis HIV-1 GENOME Diploid,