Biology 331Virology 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 SystemClass I - ds DNA genomesClass IV - ss (+) RNA genome Class V - ss (-) RNA genomeClass VI - ss (+) RNA with DNA intermediateClass VII - ds DNA with RNA intermediateWe 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 FeaturesAttachment - surface protein + host receptor Penetration - receptor-mediated entry of capsidSynthesis - new proteins and genetic materialAssembly - packaging of virusesRelease - 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 PhageTemperate - lysis or lysogeny of EscherichiaLysogeny - replication without lysisStructure, attachment, penetration like T4Early genes: ASSESS HOST HEALTH…BAD: late gene expressed, inducing lysisGOOD: 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 cytoplasmExit via Golgi AND cell membrane