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Biology 331
Virology I
Recall - non-cellular, obligate intracellular parasites
Some History
1889 - Beijerinck, Tobacco Mosaic Virus - filter
1969 - Baltimore, first retrovirus
Electron microscopy and X-ray crystallography
(mid-1900’s) required to actually see viruses.
All Viruses Contain Genetic Material
DNA or - single or double stranded (ss, ds)
ss(+) = coding, ribosome can translate
ss(-) = non-coding, complement (+) made first
Form determines replication strategy
Baltimore Classification System
Class I - ds DNA genomes
Class IV - ss (+) RNA genome
Class V - ss (-) RNA genome
Class VI - ss (+) RNA with DNA intermediate
Class VII - ds DNA with RNA intermediate
We will not be covering Class II/III
All Viruses Contain Proteins
Capsid icosahedron shells hold DNA/RNA,
Nucleocapsid directly wraps DNA/RNA, helical
Some have structural tails, functional enzymes
But - truism of virology - NONE has ribosomes
Some Viruses Steal/Contain Envelopes
Host membrane, studded with viral proteins
Make less hardy outside host, transmission
Virus Replication - Common Features
Attachment - surface protein + host receptor
Penetration - receptor-mediated entry of capsid
Synthesis - new proteins and genetic material
Assembly - packaging of viruses
Release - exit of mature viruses from cell
Cells infected = host range; some acute,
latent, chronic, oncogenic…
Class I Viruses
Virulent T4 Phage
Replication always lyses host, Escherichia
Unenveloped capsid + tail attaches to LPS
Induces contraction - DNA injected
Transcription and translation by host machinery
Temperate Lambda Phage
Temperate - lysis or lysogeny of Escherichia
Lysogeny - replication without lysis
Structure, attachment, penetration like T4
Early genes: ASSESS HOST HEALTH…
BAD: late gene expressed, inducing lysis
GOOD: DNA integrates, host passively copies
Transduction
Phage transfer of bacterial DNA between hosts
Generalized: accidental packaging during lysis
Specialized: recombinant viruses after lysogeny
Papillomavirus
For this course, Polyomavirus = Papillomavirus
Small, unenveloped, capsid, 65+ strains
DNA + stolen histones, less than 10 genes
All central dogma steps carried out by host
Transformation
If host cells not dividing, papilloma activates
CIS = integrating DNA turns on adjacent genes
TRANS = protein/T-Ag turns on distant genes
RESULT - benign warts, cervical cancer (4/65)
Pap tests, surgery, vaccine… condoms ???
Variola/Smallpox
2 envelopes, nucleocapsid/genome - 200 genes
Viral DNA & RNA Pol enzymes carried in virus
Host ribosomes translate - ALL in cytoplasm
Exit via Golgi AND cell membrane