SV40

Question 1

Stages

Answer 1

Attachment

Penetration

Uncoating

Early Gene Expression

Genome Replicatoin

Late Gene Expression

Assembly

Release

Question 2

Attachment

Answer 2

• receptor mediated - VP1 attaches to MHC1

Question 3

Penetration

Answer 3

-Endocytosis in caveolae - caveolae not acidified, instead fuse with ER membrane so virions enter ER lumen

Question 4

Uncoating

Answer 4

-virus binds to receptor on luminal face of ER membrane -binding triggers a conformational change that creates an injection port through the ER membrane -viral minichromosomes diffuse into the cytoplasm and then imported into the nucleus due to the NLS signals from the histones

Question 5

Early Gene Expression

Answer 5

-DdRp II transcribes primary transcript -the primary transcript covers the early region of genome -Transcript is then capped and polyadenylated -Differential splicing occurs producing mRNAs for T-Ag and t-Ag proteins -The early mRNAs are exported into the cytoplasm and translated -T-Ag protein has NLS and is imported into the nucleus

Question 6

Genome Replication

Answer 6

-T-Ag sends host cell into S-phase of cell cycle by binding to cellular proteins Rb and p53 -T-Ag interacts with host DNA replication proteins (made during S-phase) and re-targets them to SV40 origin (T-Ag acts as a modifier subunit- hijacking) -T-Ag has DNA helicase activity that unwinds dsDNA at origin and host factors take over -Viral genome is replicated bidirectionally (Theta mode)

Question 7

Late Gene Expression

Answer 7

-T-Ag represses early region transcription and activates late region transcription. -A single primary transcript is produced covering the late region of genome and is capped and polyadenylated -late mRNAs exported to cytoplasm and translated -Differential splicing occurs generating mRNAs for agnoprotein/VP1 and VP2/VP3 -Leaky scanning occurs to produce (VP2/3 complex) and/or efficient reinitiation of translation to produce (agnoprotein/VP1) required -all late proteins have NLS and are imported into nucleus

Question 8

Assembly

Answer 8

-Agnoprotein facilitates nuclear localization of VP1 and capsid assembly -occurs in the nucleus via nucleation of pentamers around SV40 minichromosome

Question 9

Release

Answer 9

New Virions release via cell lysis