Source: A DULTS AND C HILDREN L IVING WITH HIV/AIDS (Est. Dec 2007) deaths: 2,900,000 in ,100,000 in 2007 new cases: 2,500,000 in 2007

Adaptive immunity invading viruses or bacteria cytotoxic T lymphocyte B lymphocyte helper T lymphocyte signals antigen recognition signals Y Y Y Y Y Y Y Y Y antibody production killing of infected cells macrophage

 First identified as “RNA tumor viruses”  Blocked by DNA synthesis or transcription inhibitors ?!  Heresy: Howard Temin suggested a DNA “provirus” form was part of the replication cycle  Reverse transcriptase activity demonstrated in 1970 Retroviruses Howard Temin

 Oncornaviruses  Transform host cells  Slow viral production  Long-term association  Lentiviruses  Active killing of cells  Chronic  Long period with relatively little effect on host Retroviruses HIV budding

 ss(+)RNA  diploid: two copies  enveloped  3 major genes:  gag → capsid, matrix  pol → reverse transcriptase, integrase, protease  env → envelope protein, gp160 → gp120 + gp41  additional genes: nef, rev, tat, vif, vpu, vpr HIV

Entry  gp120, binds CD4 receptor  gp41, “fusion protein” HIV replication GP41 GP120 envelope

Entry  gp120 binds CD4 receptor on T H lymphocyte HIV replication cytoplasm of T H lymphocyte CD4

Entry  Binding causes conformational change  CCR5 co-receptor recruited  chemokine receptor HIV replication CCR5

Entry  More conformational change  gp41 unfolds, inserts into membrane  Close contact results in fusion HIV replication

Retrovirus genome:  5 ′ cap, poly(A) tail HIV replication AAAAA RU5PBPPU3R 5’3’ coding region direct repeat direct repeat

Reverse transcription:  host tRNA bound to PB site (tRNA Pro, tRNA Lys3 or tRNA Lys 1,2 ) HIV replication AAAAA RU5PBPPU3R 5’3’

Reverse transcriptase:  RNA-dependent DNA polymerase  DNA-dependent DNA polymerase  RNase H  helicase  molecules/virion HIV replication

Reverse transcription:  (−) strand synthesis, using 3′ end of tRNA as primer  RT makes DNA to 5 ′ end of genome HIV replication AAAAA RU5PBPPU3R 5’3’

Reverse transcription:  RNase H removes RNA in RNA-DNA hybrid HIV replication AAAAA RU5PBPPU3R 5’3’

R R Reverse transcription:  DNA complementary to R sequence can pair with 3 ′ R HIV replication AAAAA RU5PBPPU3 5’3’ U5

Reverse transcription:  DNA complementary to R sequence can pair with 3 ′ R HIV replication AAA PBPPU3R R 3’ U5

Reverse transcription:  DNA synthesis and RNA removal continue HIV replication AAA PBPPU3R RU5

Reverse transcription:  DNA synthesis and RNA removal continue HIV replication AAA PBPPU3R RU5 U3PB AAA PPR RU5U3

Reverse transcription:  Polypurine tract (PP) is most resistant to RNase H; serves as primer for (+) strand synthesis HIV replication PP RU5U3

Reverse transcription:  (+) strand synthesis continues; PP and tRNA eventually degraded HIV replication RU5U3 RU5U3 PB PP

PB Reverse transcription:  PB can pair with (−) strand HIV replication RU5U3 RU5U3 PP

PB Reverse transcription  Synthesis continues from both 3 ′ ends HIV replication RU5U3 RU5U3 3’ PP

Reverse transcription  Synthesis continues from both 3 ′ ends HIV replication PB RU5U3 RU5U3 PP

Completed DNA  double-stranded  both ends have U3-R-U5 = long terminal repeat (LTR) HIV replication 5’ 3’ U3RU5PBU3RU5PP LTR coding region

Integration:  DNA migrates to nucleus  Integrase enzyme cleaved from pol (RT) protein  Cuts host DNA and LTR  Host polymerase and ligase fill gaps HIV replication

Gene expression and genome replication:  U3 region contains promoter  Transcription and processing by host enzymes HIV replication U3RU5PBU3RU5PP provirus AAAAA promoterpoly(A) site transcription

Gene expression:  Unspliced mRNA → Gag  Spliced mRNA → Env  Frameshifting → Gag-Pol fusion  Protease cleaved from fusion HIV replication gag pol

Assembly and Release:  Env (gp160) inserted into membrane  Gag cleaved to make MA, NC  NC associates with RNA  MA associates with Env HIV replication

Assembly and Release:  Budding  Maturation continues after budding (protease cleavage) HIV replication budding immaturemature

“Bonus Genes”  Small proteins produced by alternative splicing  Contribute to virulence  tat: increases transcription efficiency (toxic to some cells)  rev: regulates exit of unspliced RNA from nucleus  nef: down-regulates CD4 and MHC I; up-regulates NF-  B  vpu: breaks down CD4 in ER, aids viral exit  vif: suppresses antiviral activity  vpr: transports RNA into nucleus; arrests cell division in G 2 HIV replication

 Transmitted mostly by infected cells in body fluids  Can bud/fuse simultaneously  M-tropic virus infects macrophages (using CCR5)  Carried to lymph nodes  T-tropic virus infects T H (using CXCR4)  Replicates in activated T cells  “Latent” in resting T cells  Immune response to virus actively kills cells  Actively kills cells  Replaced by rapid proliferation during chronic phase HIV pathogenesis

 Entry  gp120  gp41  CD4  CCR5/CXCR4  Uncoating  Reverse transcription  Nuclear transport  Integration Antiviral drug targets  Transcription  Splicing  Translation  Production of fxnl proteins  Assembly  Maturation  Budding